It is complicated. There are several options, each with tradeoffs in functionality, compatible software, and performance.

A simple method is to use one system as a desktop, and SSH into the others as “headless”.

Other options include making a K8s or HPC cluster (there are other cluster types).

Spreading a single set of communicating processes requires a low latency interconnect. Something better than Ethernet, like Infiniband. But many programs don’t support that.

Time to check Humble Bundle.

Me and the homes in the old person dorm. Playing games, watching movies, doing community service.

You put lots of time and effort in. Now it will be discarded due to decisions of others.

Sad and/or disappointed feelings are normal.

Take care of yourself.