Issue aside, this doesn't completely fix the titular problem in TabContainer:

The button may still end up outside bounds.

It's better than before though (beta1):

EDIT:

It works correctly when clip_tabs is disabled.

Can confirm this solves #114111

@KoBeWi Huh? It works correctly on my end, even with clip_tabs enabled:

Did you do something specific?

Nevermind, this is unrelated bug.
When you call set_popup() or change clip_tabs the TabContainer won't update minimum size.

Thanks!