If you keep your share folder on another device, you can switch instantly between versions. So if you have a stick with 5.20 and a stick with 5.21, that will not harm your data if you swap. Apart with the Dolphin config issue what
I talked about.
I think he get in trouble because everybody want everything automatic. And this is just not working with Dolphin and Dosbox where you can configurate your joystick(s) and buttons after your own need. So, if you take the configuration generated for retroarch inside this, you will be sure wrong.
I use in alot of dos games controls from player1 and player 2 together, to have more options for player 1 and a specific game. As example joystick player 2 as mouse control in games where it is needed.
And in Wiimote Emu same story to have enough controls for Goldeneye 007. With reconfiguration from your standard in Retroarch games, this cannot work. Thats the problem in 5.21.
And also I have on my bartop 2xusb Dragonrise that work very good if you let them 🙂