[c8g]

Did you consider VFS For Git and Scalar from Microsoft? What was the result? https://github.com/microsoft/VFSForGit

https://github.com/microsoft/scalar

[scarmig]

VFS for Git is deprecated, although something incorporating its approach is likely to best way to implement a real monorepo. Which AFAIK doesn't exist, outside of proprietary implementations used inside certain big tech companies.