There is an old adage: "If it's working, don't change it." Unfortunately, that is bad advice when it comes to computer security. Software is inherently ephemeral, and when a version goes out of support, it must be upgraded or replaced. When a patch appears, it must be applied, and the sooner the better because the bad guys decompile those patches to figure out what to attack.
Error message
Deprecated function: str_replace(): Passing null to parameter #3 ($subject) of type array|string is deprecated in Drupal\filter\Element\ProcessedText::preRenderText() (line 105 of core/modules/filter/src/Element/ProcessedText.php).
Drupal\filter\Element\ProcessedText::preRenderText() call_user_func_array() (Line: 107) Drupal\Core\Render\Renderer->doTrustedCallback() (Line: 910) Drupal\Core\Render\Renderer->doCallback() (Line: 441) Drupal\Core\Render\Renderer->doRender() (Line: 253) Drupal\Core\Render\Renderer->doRenderRoot() (Line: 143) Drupal\Core\Render\Renderer->{closure:Drupal\Core\Render\Renderer::renderInIsolation():142}() (Line: 634) Drupal\Core\Render\Renderer::{closure:Drupal\Core\Render\Renderer::executeInRenderContext():634}() Fiber->start() (Line: 635) Drupal\Core\Render\Renderer->executeInRenderContext() (Line: 142) Drupal\Core\Render\Renderer->renderInIsolation() (Line: 242) check_markup() (Line: 18) title_html_preprocess_field__node__title() (Line: 354) Drupal\Core\Extension\ModuleHandler->invoke() (Line: 311) Drupal\Core\Theme\ThemeManager->{closure:Drupal\Core\Theme\ThemeManager::render():293}() (Line: 340) Drupal\Core\Theme\ThemeManager->render() (Line: 500) Drupal\Core\Render\Renderer->doRender() (Line: 253) Drupal\Core\Render\Renderer->doRenderRoot() (Line: 143) Drupal\Core\Render\Renderer->{closure:Drupal\Core\Render\Renderer::renderInIsolation():142}() (Line: 634) Drupal\Core\Render\Renderer::{closure:Drupal\Core\Render\Renderer::executeInRenderContext():634}() Fiber->start() (Line: 635) Drupal\Core\Render\Renderer->executeInRenderContext() (Line: 142) Drupal\Core\Render\Renderer->renderInIsolation() (Line: 152) Drupal\Core\Render\Renderer->renderPlain() (Line: 76) Drupal\html_title\HtmlTitleFilter->decodeToText() (Line: 85) Drupal\html_title\HtmlTitleFilter->decodeToMarkup() (Line: 148) html_title_node_view() call_user_func_array() (Line: 389) Drupal\Core\Extension\ModuleHandler->{closure:Drupal\Core\Extension\ModuleHandler::invokeAll():388}() (Line: 340) Drupal\Core\Extension\ModuleHandler->invokeAllWith() (Line: 388) Drupal\Core\Extension\ModuleHandler->invokeAll() (Line: 289) Drupal\Core\Entity\EntityViewBuilder->buildMultiple() (Line: 240) Drupal\Core\Entity\EntityViewBuilder->build() call_user_func_array() (Line: 107) Drupal\Core\Render\Renderer->doTrustedCallback() (Line: 910) Drupal\Core\Render\Renderer->doCallback() (Line: 441) Drupal\Core\Render\Renderer->doRender() (Line: 230) Drupal\Core\Render\Renderer->render() (Line: 501) Drupal\Core\Template\TwigExtension->escapeFilter() (Line: 64) __TwigTemplate_d2f26875c8ac8a85a92c59d7e85552d1->doDisplay() (Line: 411) Twig\Template->yield() (Line: 394) Twig\Template->render() (Line: 51) Twig\TemplateWrapper->render() (Line: 35) Drupal\Core\Template\TwigThemeEngine->renderTemplate() (Line: 428) Drupal\Core\Theme\ThemeManager->render() (Line: 500) Drupal\Core\Render\Renderer->doRender() (Line: 513) Drupal\Core\Render\Renderer->doRender() (Line: 230) Drupal\Core\Render\Renderer->render() (Line: 501) Drupal\Core\Template\TwigExtension->escapeFilter() (Line: 89) __TwigTemplate_ee36d57d314a7f41698e259aa80d52a7->doDisplay() (Line: 411) Twig\Template->yield() (Line: 394) Twig\Template->render() (Line: 51) Twig\TemplateWrapper->render() (Line: 35) Drupal\Core\Template\TwigThemeEngine->renderTemplate() (Line: 428) Drupal\Core\Theme\ThemeManager->render() (Line: 500) Drupal\Core\Render\Renderer->doRender() (Line: 513) Drupal\Core\Render\Renderer->doRender() (Line: 230) Drupal\Core\Render\Renderer->render() (Line: 242) Drupal\Core\Render\MainContent\HtmlRenderer->{closure:Drupal\Core\Render\MainContent\HtmlRenderer::prepare():235}() (Line: 634) Drupal\Core\Render\Renderer::{closure:Drupal\Core\Render\Renderer::executeInRenderContext():634}() Fiber->resume() (Line: 649) Drupal\Core\Render\Renderer->executeInRenderContext() (Line: 235) Drupal\Core\Render\MainContent\HtmlRenderer->prepare() (Line: 131) Drupal\Core\Render\MainContent\HtmlRenderer->renderResponse() (Line: 90) Drupal\Core\EventSubscriber\MainContentViewSubscriber->onViewRenderArray() (Line: 246) Symfony\Component\EventDispatcher\EventDispatcher::{closure:Symfony\Component\EventDispatcher\EventDispatcher::optimizeListeners():241}() (Line: 206) Symfony\Component\EventDispatcher\EventDispatcher->callListeners() (Line: 56) Symfony\Component\EventDispatcher\EventDispatcher->dispatch() (Line: 188) Symfony\Component\HttpKernel\HttpKernel->handleRaw() (Line: 76) Symfony\Component\HttpKernel\HttpKernel->handle() (Line: 53) Drupal\Core\StackMiddleware\Session->handle() (Line: 48) Drupal\Core\StackMiddleware\KernelPreHandle->handle() (Line: 28) Drupal\Core\StackMiddleware\ContentLength->handle() (Line: 203) Drupal\page_cache\StackMiddleware\PageCache->fetch() (Line: 140) Drupal\page_cache\StackMiddleware\PageCache->lookup() (Line: 89) Drupal\page_cache\StackMiddleware\PageCache->handle() (Line: 206) Drupal\cleantalk\EventSubscriber\BootSubscriber->handle() (Line: 50) Drupal\ban\BanMiddleware->handle() (Line: 48) Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle() (Line: 51) Drupal\Core\StackMiddleware\NegotiationMiddleware->handle() (Line: 53) Drupal\Core\StackMiddleware\AjaxPageState->handle() (Line: 54) Drupal\Core\StackMiddleware\StackedHttpKernel->handle() (Line: 745) Drupal\Core\DrupalKernel->handle() (Line: 19)Deprecated function: str_replace(): Passing null to parameter #3 ($subject) of type array|string is deprecated in Drupal\filter\Element\ProcessedText::preRenderText() (line 105 of core/modules/filter/src/Element/ProcessedText.php).
Drupal\filter\Element\ProcessedText::preRenderText() call_user_func_array() (Line: 107) Drupal\Core\Render\Renderer->doTrustedCallback() (Line: 910) Drupal\Core\Render\Renderer->doCallback() (Line: 441) Drupal\Core\Render\Renderer->doRender() (Line: 253) Drupal\Core\Render\Renderer->doRenderRoot() (Line: 143) Drupal\Core\Render\Renderer->{closure:Drupal\Core\Render\Renderer::renderInIsolation():142}() (Line: 634) Drupal\Core\Render\Renderer::{closure:Drupal\Core\Render\Renderer::executeInRenderContext():634}() Fiber->start() (Line: 635) Drupal\Core\Render\Renderer->executeInRenderContext() (Line: 142) Drupal\Core\Render\Renderer->renderInIsolation() (Line: 242) check_markup() (Line: 18) title_html_preprocess_field__node__title() (Line: 354) Drupal\Core\Extension\ModuleHandler->invoke() (Line: 311) Drupal\Core\Theme\ThemeManager->{closure:Drupal\Core\Theme\ThemeManager::render():293}() (Line: 340) Drupal\Core\Theme\ThemeManager->render() (Line: 500) Drupal\Core\Render\Renderer->doRender() (Line: 230) Drupal\Core\Render\Renderer->render() (Line: 501) Drupal\Core\Template\TwigExtension->escapeFilter() (Line: 62) __TwigTemplate_cf92a79970a6226d5155a7d1b269bcaf->doDisplay() (Line: 411) Twig\Template->yield() (Line: 394) Twig\Template->render() (Line: 51) Twig\TemplateWrapper->render() (Line: 35) Drupal\Core\Template\TwigThemeEngine->renderTemplate() (Line: 428) Drupal\Core\Theme\ThemeManager->render() (Line: 500) Drupal\Core\Render\Renderer->doRender() (Line: 230) Drupal\Core\Render\Renderer->render() (Line: 501) Drupal\Core\Template\TwigExtension->escapeFilter() (Line: 64) __TwigTemplate_d2f26875c8ac8a85a92c59d7e85552d1->doDisplay() (Line: 411) Twig\Template->yield() (Line: 394) Twig\Template->render() (Line: 51) Twig\TemplateWrapper->render() (Line: 35) Drupal\Core\Template\TwigThemeEngine->renderTemplate() (Line: 428) Drupal\Core\Theme\ThemeManager->render() (Line: 500) Drupal\Core\Render\Renderer->doRender() (Line: 513) Drupal\Core\Render\Renderer->doRender() (Line: 230) Drupal\Core\Render\Renderer->render() (Line: 501) Drupal\Core\Template\TwigExtension->escapeFilter() (Line: 89) __TwigTemplate_ee36d57d314a7f41698e259aa80d52a7->doDisplay() (Line: 411) Twig\Template->yield() (Line: 394) Twig\Template->render() (Line: 51) Twig\TemplateWrapper->render() (Line: 35) Drupal\Core\Template\TwigThemeEngine->renderTemplate() (Line: 428) Drupal\Core\Theme\ThemeManager->render() (Line: 500) Drupal\Core\Render\Renderer->doRender() (Line: 513) Drupal\Core\Render\Renderer->doRender() (Line: 230) Drupal\Core\Render\Renderer->render() (Line: 242) Drupal\Core\Render\MainContent\HtmlRenderer->{closure:Drupal\Core\Render\MainContent\HtmlRenderer::prepare():235}() (Line: 634) Drupal\Core\Render\Renderer::{closure:Drupal\Core\Render\Renderer::executeInRenderContext():634}() Fiber->resume() (Line: 649) Drupal\Core\Render\Renderer->executeInRenderContext() (Line: 235) Drupal\Core\Render\MainContent\HtmlRenderer->prepare() (Line: 131) Drupal\Core\Render\MainContent\HtmlRenderer->renderResponse() (Line: 90) Drupal\Core\EventSubscriber\MainContentViewSubscriber->onViewRenderArray() (Line: 246) Symfony\Component\EventDispatcher\EventDispatcher::{closure:Symfony\Component\EventDispatcher\EventDispatcher::optimizeListeners():241}() (Line: 206) Symfony\Component\EventDispatcher\EventDispatcher->callListeners() (Line: 56) Symfony\Component\EventDispatcher\EventDispatcher->dispatch() (Line: 188) Symfony\Component\HttpKernel\HttpKernel->handleRaw() (Line: 76) Symfony\Component\HttpKernel\HttpKernel->handle() (Line: 53) Drupal\Core\StackMiddleware\Session->handle() (Line: 48) Drupal\Core\StackMiddleware\KernelPreHandle->handle() (Line: 28) Drupal\Core\StackMiddleware\ContentLength->handle() (Line: 203) Drupal\page_cache\StackMiddleware\PageCache->fetch() (Line: 140) Drupal\page_cache\StackMiddleware\PageCache->lookup() (Line: 89) Drupal\page_cache\StackMiddleware\PageCache->handle() (Line: 206) Drupal\cleantalk\EventSubscriber\BootSubscriber->handle() (Line: 50) Drupal\ban\BanMiddleware->handle() (Line: 48) Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle() (Line: 51) Drupal\Core\StackMiddleware\NegotiationMiddleware->handle() (Line: 53) Drupal\Core\StackMiddleware\AjaxPageState->handle() (Line: 54) Drupal\Core\StackMiddleware\StackedHttpKernel->handle() (Line: 745) Drupal\Core\DrupalKernel->handle() (Line: 19)