Hi Roman,

1. Problem can be with PHP version. Please switch to PHP 8.3 or PHP 8.4 and try again. Please do not use PHP 8.5 yet!
2. Check if you can upload the same image file using Joomla Media Manager.
3. Try also different browser, just for testing purposes.

Hi, Paul.

1. I use PHP 8.4, so that's not the issue.
2. Yes i can upload image using Joomla Media Manager but i see similar problem : https://ibb.co/7dmb8FPc
3. I use it all the time Chrome , i try it on Edge but i see same issue .

Edge use also Chromum engine, the same as Chrome.

ok i try it on Firefox and i see same problem . here is screen from console : https://ibb.co/fhDDjfF

During the weekend I cannot ask our developers for technical advice, but please share access to admin area, so on Monday morning I will ask and let you know, Ok. By now focus on other areas.

Becuase as you mentioned, you have the same problem also in Joomla Media Manager, please make research/ask on forum.joomla.org

Joomla System files, as you see:

I am more then sure that somebody had the same issue before, and J! community found a reason/fix.