[kdndnrndn]

I'm not aware of any optical mouse using a general purpose MCU, to my knowledge they are all using ASICs

[bigfatkitten]

There are millions, if not tens of millions of USB and PS/2 keyboards and mice out there powered by Cypress MCUs with 8051 cores.

[Tajnymag]

That's a lot of cores

[sweetcocomoose]

Nordic dominates the market for keyboards and mice. Programmable MCUs with BLE radios are required for any wireless devices.

[Rohansi]

Some gaming mice do for running RGB lights, macros, or whatever.