We're starting to have the conversation of "do we need to replace GitHub as our CI/CD pipeline?" No idea if/when we decide to pull that bandaid but I think once we can't merge a hot fix into main because of GH being down, it'll be a big org push to replace it. What's everyone else using? Self hosted Gitlab? Gitea?
If your app is not too large you can do CI/CD perfectly fine from your laptop. Put it in a docker container if you want to ensure it is perfectly reproducible. You still need Github as the origin repo to pull from, but the "git part" of GitHub seems to be (almost) always up and running. (We use "capistrano" for this)
Not if you want to make sure it compiles and works on Windows (which you don't have) or macOS (which you don't have and can't emulate). That's something github gives for free, and for me, it's the only reason to stay on github for small/tiny free software projects (at least as a secondary host).