Normally while you’re looking at the steam UI, you can use CTRL-1 for the steam menu or CTRL-2 for the performance/other options (menu on the right). You can use a controller as well by pressing on the guide (xbox) button for the steam menu and guide + A (or X on a playstation controller) for the right menu.
However, this does not work in-game for me, so I posted a topic about it here because I just can’t seem to get it to work: Any way to get the overlay in gaming mode while in-game? CTRL-1/CTRL-2 or Guide button not working - General - Universal Blue (universal-blue.discourse.group)