UltraEdit for Windows has the two options Minimize on last file close and Minimize on system tray (not taskbar) at Advanced - Settings/Configuration - Application Layout - Window State. The second setting is definitely Windows specific while the first one could also exist for UltraEdit for Mac. Can you find in Preferences of UltraEdit for Mac a similar setting or a setting related to application quit?
Best regards from an UC/UE/UES for Windows user from Austria
Thanks for trying but none of that is related (checked).
Further testing.
File -> Quit = Works
CMD-Q = Works
Right click on icon in finder bar and select Quit = Doesn't work
Alt right click on icon in finder bar and select Force Quit = works.
I suggest to report this issue to IDM support by email as this is a Mac specific issue which most likely must be fixed by a developer of UltraEdit for Mac.
Best regards from an UC/UE/UES for Windows user from Austria