@foone The sol 3 has two stm32 inside (it's a split keyboard so one on each side). It's fun because only one really is used at the same time (the other acts more as a muxer to send keys to the primary one through serial). But both are fully capable of acting as the primary, so you can flash two different firmwares on them, and depending on which side you plug in you kind of have two different keyboards.
It also means you need to always plug in the same side if you want to keep the same configuration.