We are a team of 60+ developers working on the same product and are moving from SVN to Git and GitHub. We have a process in SVN where in individual files are locked and when
this is possible. git-lfs 2.0 introduces the ability to lock files: see these links: https://github.com/git-lfs/git-lfs/wiki/File-Locking. Support for this feature is available starting from TFS 2017.2: https://docs.microsoft.com/en-us/vsts/release-notes/.
Not exactly locking, but Github has introduced a concept called "Code Owners". Allows you to restrict part of your codebase to only allow commits after review by the code owners