Thank you very much for your answer :)

I have already read Microsoft's documentation on a TabView within a title bar. The problem lies with the system caption buttons. I prefer to use my own caption buttons, and that's exactly where the issue arises. When I set a MinWidth for the tab strip footer, the tabs no longer overlap the caption buttons.

However, I end up with a strange effect where the tabs do not reduce their width correctly. The "+" symbol doesn't stay at the caption button, but instead stays earlier and then bugs out, moving in small steps until it reaches the caption button, and then it stops.

I haven't seen this behavior in browsers, for example. In browsers, the "+" stays directly next to the caption buttons, and only then do the tabs start to lose width.