Where do the projects move to if they've been banned from Github?

Edit: Where would they host it and not get taken down by DMCA?

https://tangled.org/ or https://gitflic.ru/

GitLab should be the closest comparable one. After that there are a bunch of smaller hosts for different niches.

There no lack in choice if you search, especially for these kind of project that don't need a ton of tool integration or CI/CD tools.

Is there anything like bittorrent for github repos?

That was always the appeal of people exploring shared compute and storage on crypto networks, it was overhyped and burdened by the financial speculation (though I imagine it also helped fund development), because the cool thing for me was people trying to build resilient distributed systems that protect from these kinds of issues

Self host? Github isn't a monopoly

Setting up forejo on a VPS takes an hour, at most, for someone who has already done it a couple of times.