Hello,
I just came across this repository: https://github.com/Stan6314 where Stan has emulators for ZX81 and ZX-Spectrum.... Can we use them for our board??
If it works with the original FabGL board it should work with ESP32-SBC-FabGL. For ZX-Spectrum also check this blog post:
https://olimex.wordpress.com/2023/05/31/zx-espectrum-emulator-tested-with-esp32-sbc-fabgl-the-mensch-computer-with-w65c256-got-vga-display-and-keyboard/