For Joomla 5.4.3 users experiencing a flashing problem when editing content using tinyMCE the files contained here will fix it for you. They are the same files that will be available in the next release of Joomla so they are safe to install.
Download the zip file and extract the contents and then upload tinymce.js and tinymce.min.js to your site into the media\plg_editors_tinymce\js folder to replace the two files with the same name.
Important
If after replacing the two files and clearing the browser cache you still have problems then your site is using the gzipped version of the javascript which is NOT included in the update. You should delete the file media/plg_editors/js/tinymce.min.js.gz to ensure that the correct hotfix files are being used by your site