I think, macOS native select menu could and should be used here? The custom menu with face corners doesn’t look good. Why even bother to remake something that already exists?
But why? Why would make a form that is trying to be a menu? They have exact same functions. As a user these type of decision are always bit strange. This custom form menu is now worse in every way (looks and usability). At least it should be same or better, right? Now you can’t for exmple use arrow keys to navigate the menu. And there are probably plenty more usability trade-offs, that I don’t even know about.
Understandable, but of course I hope that you considered having a os menu + something else for the “more you needed”. Or better yet, if you were to consider this in the future…
For example, if you now try to match the user experience of the OS menu, you will likely lose many or even all of the benefits you gained in the first place.