Asus C302C Cave - what's best to do?

End of support so should do something. Installed Mrchromebox’s new firmware, tried Windows 11 but many missing drivers. Installed ChromeOS Flex, everything works except audio. What’s best to do? I would like the built in audio back. I could put it back how it was, I made a restore SD Card from the last Cave stable release, but how to flash the firmware back again? Or is there a better option?

Thanks

So far Ultramarine Linux works fine, audio too with the script in Chultrabook documentation.