Shameless self-plug and probably not what you're looking for, but anyway: I've created https://github.com/abuob/yanice for that sort of monorepo-size; too many applications/libraries to be able to always run full builds, but still not google-scale or similar.

It ultimately started as a small project because I got fed up with NX' antics a few years back (I think since then they improved quite a lot though), I don't need caching, I don't need their cloud, I don't need their highly opinionated approach on how to structure a monorepository; all I needed was decent change-detection to detect which project changed between the working-tree and a given commit. I've now since added support to enforce module-boundaries as it's definitely a must on a monorepo.

In case anyone wants to try it out - would certainly appreciate feedback!