Wouldn’t unlocking the bootloader and installing a custom ROM be easier, more stable and cheaper than buying a niche product that’s unlikely to work properly?

What exactly are you looking for? Android IS Linux, do you want to try a different “distribution” just for fun?

The code is still accessible, you just can’t use the code search function in the web, which normal git doesn’t have anyway.

The latest pixel devices (since 6 I think?) already provide accees to a /dev/kvm device, so maybe you could even run a normal Ubuntu server VM on your phone for hosting these services.

Are you sure the content is gone? I assume the communities had users from other servers, if so isn’t the content replicated on other servers?