Steps to reproduce the issue

1. Upload image with special charaters with czech letter(or special letters), via Total Commander, Filezilla etc.
2. In admin, make new article and then open in tinymce editor CMS Content / Media and select that image with czech letters
3. Save that article

Expected result

Saving that article.

Actual result

500: whooops

/www/libraries/vendor/joomla/string/src/phputf8/mbstring/core.php (line 96)
or www/libraries/vendor/joomla/filter/src/InputFilter.php (line 277)

Error: Maximum execution time of 60 seconds exceeded

System information (as much as possible)

PHP 7.4.4
Joomla 4.0.4

Additional comments

When you upload image via Media in admin, everything goes well. It will rename special letters.

I dont see this as an error/bug, but maybe there is a way to let user know, where exactly is the problem. In the name od that uploaded(via FTP) image/file with special letters.

Try this in article content and you will see

testovaci tšext