it’s built upon/by the same devs as forgejo, which is open tech to self host your own git server (with federation potentially coming), so supporting one supports the other
Codeberg is a German non profit iirc, I host some stuff there but most is on my personal Forgejo.
The Forgejo devs (mostly centered on Codeberg) are also the ones pushing for federalized code forges (I open a PR on your git server from mine and so on)
To work on it from different devices, use features like issues, basically the same reason people use it for public repos instead of just uploading it as a zip somewhere. Sometimes you have stuff you don’t want to release to the public or it’s just not ready to release to the public yet.
Gitlab.com just started doing shady stuff and requiring phone numbers or something on sign-up if what I read a few days ago here, is correct. For self-hosting the software should still be alright.
Github.com is by Microsoft and not free software. I don’t know what direction Microsoft is taking with it, but it is widely adopted and they give you free CI and other stuff.
Codeberg, Sourcehut etc should be fine. I haven’t heard negative things about them.
“Best” is running my own Forgejo on my server. At least that’s what I think. But I also keep things on github, since all the people are there.
It is git. You can fork repos. And some platforms can mirror a repository and keep it synced. If not, you’d need to build something with webhooks. Or keep both synced manually every now and then (or on a new release/tag.)
From personal experience, if you’re hosting Gitlab and make it available to the internet, make sure to keep it updated or your server will be super slow hosting a crypto miner within a year.