Huh, TIL that Gowin sells one of their small FPGAs with an integrated Cortex M3 core? The part number is GW1NSR-**4C*, and the "C" variant is the one with the Cortex M3. LCSC has about 300 of them in stock for ~18 EUR each. Here's a chinese datasheet:

https://www.lcsc.com/datasheet/C7570393.pdf