I am very busy redeveloping my application for Joomla 4, it is not easy. It is on my own computer running the latest of everything. I won't be finished until you are able to update Modal.
When I use the AMM, I get this warning all the time:
Warning
: Undefined array key "Joomla\CMS\HTML\Helpers\Bootstrap::startTabSet" in
/home/opt/eluceo_ishine/libraries/src/HTML/Helpers/Bootstrap.php
on line
860
Warning
: Trying to access array offset on value of type null in
/home/opt/eluceo_ishine/libraries/src/HTML/Helpers/Bootstrap.php
on line
860
Warning
: Trying to access array offset on value of type null in
/home/opt/eluceo_ishine/libraries/src/HTML/Helpers/Bootstrap.php
on line
860
I am sorry I cannot publish online as my version is still full of other errors and additional development which will take me most of the rest of the year to fix. It has taken me this week just to get the front page working again.
In my coding, I check the objects before using them so that they don't create serious failures later on.
I cannot reproduce the issue you name. You mention your setup is still full of errors. So that suggests there might be stuff seriously wrong/broken in your setup.
But if I can't see the issue and test things, I can't know what is causing the error you mention in Advanced Module Manager.
If you can reproduce this on an online environment to which I can get access, I am happy to look into this further.
99% of the core in my application is now working, I am now fixing the front end.
As I am developing I use error reporting. I am on php 8.1 so the Joomla produces rather a lot warnings and notifications, so I keep the reporting on simple.
When I changed it to none, the errors on the AMM went away, i.e. not reported.