That doesn't require any external tools even. All that information is in the repository already.
Here's an example of commits(==changes) in between "v20.1C.6" and "v20.1C.6-update-2" using just
the github:
TSDZ2 Open Source Firmware adapted to VLCD5-VLCD6-XH18 displays - Comparing v20.1C.6...v20.1C.6-update-2 · emmebrusa/TSDZ2-Smart-EBike-1
github.com
From there you can click "Files changed (103)", and it will list the actual changes into files instead of
just commits that should describe those changes.
And once you have it cloned on your machine, you could just use git for the commit logs(/commit diffs).