I cannot upload a video in my Gallery Tab.

Then my guess is an error is happening that's preventing it from working. Check server error logs to see if maybe it's a server side error. If you've any security extensions installed (either in Joomla or PHP) check their logs to see if it's rejecting it. Sometimes a mod_security rule will prevent submitting external URLs for example.

There's nothing more I can do without access to investigate the issue so you'd need to PM backend super user login credentials and will like need to install a debug build to force some error output.

Problem solved.  Thanks for sending me in the right direction,
For your information here is my discussion with the Hosting Department and the solution.Works beautifully!! Thanks for your persistence in getting this to work.
I have already uploaded a video.
Posted by Beat on 7th December 2023 (02:32)OperatorHi Carmelo,We just added another exception in our firewall ruleset because a different rule made a false positive.Please retry now and let us know if it now works for you.We are here to help you !Best Regards,
Beat    
Posted by Carmelo Esposito on 6th December 2023 (21:23)OwnerI cannot seem to find this, Logs and Reports" / "Apache error log",
Can you please let me know where it is?
Posted by Carmelo Esposito on 6th December 2023 (21:19)OwnerI just tried again a few times and it did not work.
Here is an example link I tried to upload.
xxxxyyyyyxxxzzz
Posted by Beat on 6th December 2023 (18:20)OperatorHello,Yes, it was a false positive of our application firewall (ModSecurity).We have added an exception for this valid post request.Please try again and confirm if it's working.We are here to help you !Best Regards,
BeatP.S. You can see anytime server-side error logs at your hosting panel in "Logs and Reports" / "Apache error log", and see if there are errors, but make sure that they are from your own IP address, as most attacks will be logged there.