Most people run to GitLab or Codeberg. The real loss is network effect of everyone being on GitHub.
GitLab: most similar to GitHub. Repos, CI/CD, issues. Hosted or self-host
Codeberg: free, non-profit, FOSS-friendly. Runs Forgejo. Where Zig went
Forgejo / Gitea: lightweight, self-host on a small server
Bitbucket: fine if you're already in Atlassian/Jira land
Sourcehut: minimalist, email-patch workflow. Fast but a culture shift
Radicle: peer-to-peer, no central server. Niche, principled
Tangled: newer, built on ATProto