Wireless controller maker 8BitDo have innovated again with 8BitDo DIY, a series of mods that can be installed into existing NES, SNES, or Genesis controllers to turn them into Bluetooth controllers. You just disassemble the controller, remove the PCB, and replace it with the 8BitDo PCB. The Tom's Hardware article linked below states the controllers are compatible with Windows, macOS, Raspberry Pi, Nintendo Switch, and more.
For those that wanna read more:
https://www.tomshardware.com/news/8bitd ... 37468.html