Talking about RP2040 powered controller firmware. GP2040 is an amazing project, which is used a lot in the Fighting Game Community where custom controllers are common. https://github.com/OpenStickCommunity/GP2040-CE
I once tried putting an Arduino in an arcade stick, for reading controller inputs and sending keyboard presses via USB, but the lag was horrible. It's been on my to-do list to eventually dive enough into AVR-C to try to improve on it.
There is/was a premade board for this (don't remember what it was called), but it was quite expensive, and I didn't want to keep moving it between controllers.