I’m kind of surprised by the amount of comments. Thanks for helping 
- I’m on windows 10 (and also ubuntu, which I’m currently not using for photos, but more for development)
- I’m using darktable 3.4.0
- exiftool is a solution from outside darktable. I wasn’t aware that it could manipulate xmp files, but it seems like a good idea for an external tool.
- The Make/model of camera is also not available. The photos were taken by a professional who erased all meta data. There isn’t anything I can do about this.
- The files were imported via the “folder…” button
I just checked out the darktable source code and it seems like it should be possible to add editing of the creation date to the metadata module…