Javascript Error 404

Excuse me for my bad English !
I have started to create my site and I am having problems with Beaver Builder.
Beaver Builder Lite does not work (it has never worked), here are the attached errors sent to the console as soon as I click on a block :

[Log] Javascript Error
[Log] AJAX returned HTML page instead of data. (Possible 404 or max_input_vars)
[Log] PHP Version: 7.3.27
[Log] Memory Limit: 512M
[Log] max_input_vars: 16000
[Log] modsecfix: Disabled

I saw that this could be from permalinks, I went into simple tuning, I have no other active extensions, and I cleared the cache. I also modified the .user.ini file by putting it “php_value max_execution_time 300”. It works a little better but not totally
I also removed the extension to reinstall it but nothing helps.
I really don’t know what to do, I need your help!
thank you so much

First suggestion is to start here: