When the menu opens in game, click on settings then set it to tab in the top section in the settings section. Or put whatever key you want to open and close the menu instead of F7.
so i literally just go to settings in the menu, set it to whatever key i want, then just press that key? edit that happened instantly: i still dont get it but ill try anyway edit 2: its set to tab by default and idk what to do to actually use the mod menu