It has never been easier to setup Proxmox, Kubernetes, and Actions Runner Controller (ARC) to do your own CI on old hardware you might otherwise recycle.

This is good advice for organizations but if you are an individual GitHub user there is no way to have a pool of a few runners available for all of your repositories.

I don't know why but individual users have to create a single instance runner and mate it with exactly one of their repositories.

Converting from an individual user to a GitHub organization is not simple. The docs certainly make it look that way but I have yet to run into anybody that has done so without some form of catastrophic error that requires support to fix

We ran actions runners ourselves in kubernetes at previous jobs, and at least back then, a lot of the errors came from the github services simply not telling the runners to handle jobs. So in general it didn't matter how much compute you had, they never got scheduled jobs.

Yep. Proxmox, Kubernetes, ARC, and t3 code threads spawned inside of kata containers is my current workflow.