Generating a own Popup

Hey there,
im trying to get a popup done by myself, if i press a GUI Button i would like to get a Popup where i could have some checkboxes and monitoring some pressure inputs. I tryed to find something about the topic here but i didnt really found anything, is there a topic that already deals with this topic? Or is there someone who tryed something like that? Ive created my own .ui File, and tryed to implement it once by the main handler what just leaded a lot of crashes, then i tryed a own handler for the ui what in my opinion is the cleaner way, but sadly same result. i didnt touch any old code in the handler but it still crashes on a buttons i never touched or created myself.

Thx for any help