It could be that your template or some other extension is conflicting with Advanced Module Manager, causing it to ignore everything Advanced Module Manager is trying to do.
See if you can reproduce the issue with the core Joomla template and/or on a clean Joomla installation with just Advanced Module Manager installed...
Yes, here is what I just posted with Gantry/RocketTheme:
Yes, working in Joomla 4.4.0 but not working in Joomla 5.
In Joomla 5:
Here is what I did. This is repeatable.
The same Advanced Module Manager was not working, as described.
I then changed the template to Cassiopia, as a test.
Advanced Module Manager worked perfectly.
BUT, when I then switched back to the RocketTheme theme, Studious, Advanced Module Manager started working.
It continues to work.
There is definitely something going on with Joomla 5 and Gantry v5.5.17
The Gantry team has asked me to ask you the following:
Does AMM have a debugger you can turn on to try and get some logs as to what's happening under the hood?
If AMM is throwing an error or otherwise has debug info related to a particular Gantry file we can look at the change history on that specific file and see what's what.
No, Advanced Module Manager doesn't have a special debugger.
Advanced Module Manager is not throwing an error.
The issue is that Gantry is overriding what Advanced Module Manager is doing.
Probably because they are both trying to do stuff via the prepareModuleList event.
And Joomla 5 has somewhat of a bug (they call it a change) regarding the prepareModuleList event.
See:
github.com/joomla/joomla-cms/issues/42149
That might be the cause of this. But I don't know what Gantry does under the hood, so... ???