The "small game console with an OLED screen" is practically a genre already. There are dozens of such projects, with all kinds of microcontrollers on board. I decided to do one more iteration on this design, using all the experience I gained recently with power circuits for such boards. Since the microcontroller wasn't the interesting part here, I just left a Seeed XIAO footprint on the back, so you can use any XIAO board – that gives you a rich selection of microcontrollers to choose from, including some 3rd party designs like the MIAO board.
For the prototype I used an RP2040 XIAO, running CircuitPython, and since I didn't have time to write special games for it, I just ported my PewPew library to it, so that I can play all the PewPew games on it in their 8x8 pixel glory. The speaker is currently unused, but it works either with PWM or audiopwmio.