If you’re in desktop mode, you have to press and hold the menu button (three horizontal line button at the top right) to switch to “gamepad” mode and actually utilize the inputs correctly. There should be a little prompt that pops up to tell you that the mode was switched. In this mode, you wont be able to navigate the desktop mode as a mouse but the buttons will work like a gamepad should. You can press and hold menu again to switch out of gamepad mode. Might need to re-map your buttons again while in gamepad mode to make sure they work the way you want them.
The JSAUX shells are significantly heavier…I used to run purple one on my LCD steam deck and vs the OLED, it was a huge difference. I’m keeping the OLED in its stock shell until we get more shells available and hopefully light weight ones.