Additionally, the up-down arrows are drawn even when the button isn’t hovered over.
Hmm prior to Tahoe the arrows did draw even when the mouse wasn't hovered inside. Upgrading to Tahoe this does not happen. I just verified this change in behavior in a test project (using the code from my previous post):
Add UIDesignRequiresCompatibility to Info.plist and set it to YES.
Run the app.
Arrows draw even while mouse is not hovering over it.
Change UIDesignRequiresCompatibility entry back to NO and the arrows do not remain. So they changed stuff in macOS 26. Maybe there is a way you to get the pre Tahoe behavior if you play with some of the button properties. Someone from Apple should know.
If there is no way to get this behavior for "free" on Tahoe you could always subclass. I don't think it should be too hard.
. In the SwiftUI.Form style, the pop-up button shrinks its width to match the width of each option when the selection changes
IMO I don't think a pop up button should adjust its width based on its selection b/c that can create a moving target for the user. I think it should take the width of its widest entry, or settle on a reasonable width and if there is an option with a long title let it truncate if that one option is selected. But what do I know I'm just a peasant developer :)
You could resize on selection change if you want though.