Opening an existing project in Xcode 10; source control not working?

I just got my new Mac and opened an existing project of mine (which is on OneDrive) in Xcode 10. When creating and coding this project on the old Mac I used the build in Source Control (Git) to commit changes (locally). On the new Mac however, all files are listed as modified and I have to commit all of them again. The commit history is present though ... How comes? How do I get Xcode to pick up the commit history of a previously created project, so files will not show up as modified ?