Yes - it was a mod_security rule - I've seen it with a couple of times now with Joomla 4 modules that want to create or edit css.
By the way, there is still an issue with the Licence / Extensions Manager CK and Brave, even with Brave's shields turned off for the site, so I'm sticking with Safari for now.
thanks for the info, I confirm that mod_security can cause some problems
concerning Brave, you can use it, as said even if it does not detect the licence, the extensions are working
the licence is used to update them
