The gameboy turned out to be no gameboy at all - its logo says Powkiddy, and it has rather more buttons than the original. There are some notes underneath.
Allwinner F1C100S @ 533mhz CPU, 32 MB DDR1 RAM, 2.8" IPS 320x240, BL-5 battery, USB-C charging port. About €30 from AliExpress.
Lacks the required pull-down resistor for USB-C to USB-C charging; will only charge with an USB-A to USB-C cable.