Is it possible to share folders without the folders being Git repositories themselves?

I have described my situation [here](https://stackoverflow.com/q/75191754/1271772). It seems clear that if the "shared folders" were `submodules`, `subtrees`, or `subrepos`, then Repo 1 and Repo 2 can both enjoy possession of them, but if I have 1000s of shared folders, I don't want to make each of them a Git repository, and neither do I want to make a third Git repository just for the common folders. Is there a way to do this in Git?

I also asked this question here: https://github.com/ingydotnet/git-subrepo/issues/573