Many users cannot currently edit Steam profile showcases due to a bug. This is likely caused by recent updates or server issues. You can try restarting the Steam client or clearing your browser's cache for a temporary fix. For the all achievements showcase, removing and re-adding it might help. Advanced users can use a browser's developer console with the setshowcaseconfig command for the game collector showcase. The most reliable solution is to wait for Valve to release a fix.

I found that changing the language fix the problem lol