You used to be able to put files and folders in multiple places in google drive. It was either removed or made a more obscure feature because I can’t find it now. I suspect it’s too confusing to maintain long-term, leading to what appears to be buggy behavior.

I handle this by making a google sheet for a project with links to the main files, many of which inevitably are cross-referenced to other projects or standards. It works well enough, and has a killer feature: if you move or rename a file, which I do all the time if documentation is refactored, the link doesn’t break!