I've used GitLab and Azure DevOps professionally, but there are a lot of services out there which host Git repositories. GitLab can also be self-hosted which is nice. They all fundamentally work the same though from my experience - code viewer, issue tracker, pull requests, some way of doing CI/CD, and various collaborative and documentation features (wikis, discussion areas, permission management, etc).

It may be good to understand also where the separation lies between features that are part of Git vs those which are part of the service you're using (like GitHub). For example, branches are Git, while pull requests and wikis are GitHub.