Sipeed lichee pi 4A… It’s only a SBC, but

• it’s quite capable

• it comes with Debian pre-installed, and

• the design of the open standard RISC-V processor cores is published.

It’s worth checking out the UK-based company Punch Technology. They build custom computers based on the specs/requirements you give them.

We bought our family desktop from them and were very happy with the service. They spent time walking through what we were looking for, how we planned to use it, and addressed all of our questions and concerns.