For RTS (especially AoE II DE) I use them as:
- the SHIFT key(create 5 units instead of 1 when hold)
- activator for a different action group, where the joystick are mapped to a circular menu. E.g. one of these menu assigns units to one of the 6 quick groups in my circular menu, and I can then select these units with just the right joystick (no button pressed). Another one activates a right joystick circular menu to go to a building (and I did map nearly all building types…)
I can also combine these, to e.g. select all barracks
I’ve been using Fladder on my steam deck, it allows downloading for offline play. Works pretty well but the interface is too mobile centric IMO.
There was Jellyflix which had a similar feature but it wasn’t straightforward to get running on Linux. Haven’t checked it since!