Flyouts used to be hardcoded to handle blocks and labels, now we have the ability to have arbitrary items in flyouts with the FlyoutInflater design (see design doc here Arbitrary items in flyouts)

The flyout base class still does some special handling for variables, in particular it fires variable creation events manually since the events are disabled during flyout creation. The doc linked above says:

Currently the flyout has some logic to fire variable creation events after the flyout is populated, because it disables events while it is being populated. I don’t think disabling the events is actually necessary, because it only changes the order of undoable events relative to UI events (not undoable events relative to each other). But this should be verified during actual implementation.

This may or may not be related to #9486 (not actually related but whatever solution we have for this might impact the solution to that or vice versa)