Git won't let me rebase (untracked files would be overwritten). What should I do?

Solution was to remove the submodule from main repo (unsubmodule). Then it was possible to do rebase.

For me rebase used to work fine even with untracked files until I did some unusual steps day before (resetting head on different branch etc.), and suddenly rebase on different branch (onto master) stopped working.

This helped:

git fetch --all
git reset --hard origin/master

Credit: https://ageekandhisblog.com/git-force-overwrite-of-untracked-working-tree-files/