how to resize controls when the window is maximized

If this is WPF, I'd say: "full speed ahead," but, if this is Win Forms:

About 7 days ago, in the context of a Windows Form Application, there was a similar question, and you might find my dialog (in the comments) with the OP, and my posted (outline of a) "solution" useful: [^].

You may also find the discussion on this QA question relevant: [^].

But, I advise you against attempting dynamic re-sizing and re-positioning of Win Form Controls unless absolutely necessary: imho, too much work for too little a return, and a good chance that arbitrary re-sizing will result in a UI that looks terrible.

You can usually get pretty good results using the standard Control properties 'DockStyle, and 'Anchor. And, do you really want to try and scale things like Fonts where they may not look very good at certain point sizes because of the way that "optical size-based hinting" works ?

If the task at hand was to make sure that my Form looked proportionally re-sized in only two cases: "normal" view, and "maximized" view, I would approach that by simply calculating two layouts, and switching them as the Form's SizeChanged Event was triggered.

If you want help with that, just ask.