If I use the link icon from the toolbar, the link management window opens; if I use the file icon in the top right, near the email address icon, the file manager window opens but remains empty or displays only a few buttons, depending on the site, ad obvusly it is impossible select a file.
See the attached screenshots.

If I use the file manager icon from the toolbar everything is ok.

Tested in Joomla 3, joomla 4, Joomla 5, Joomla 6 with JCE Pro 2.9.99.7

I'm facing the same problem. Turning off the compression of Javascript hasn't solved the problem in my case. Going back, again, to JCE versione 2.9.9.6

For me turning off SCC and JS compression solved the problem, but It worked previously. And I find it curious that the behavior in File Manager is different... I thought they used the same system. I hope compression can be re-enabled in the future.
Maibe in JCE 3 ? 😇 
Thanks!

Hi there. Same problem here with JCE 2.9.99.7. Turning Compress CSS and Compress JavaScript to No does fix the problem, this seems like a short-term fix. Is there a proper fix for this planned?