Notion is more than 10k typescript files and we view typecheck slowness and memory pressure as an existential threat to our codebase. Right now our typecheck needs ~12GB of heap size but the memory needs have accelerated recently.
NX likely would do magic for you all but I imagine it is far too late to do anything about that.
We had a very large Angular 10 project that we replaced with an NX Angular project late last year. We went from ~6 minute prod compile to around 20 seconds, recompile is lightning fast because it only builds your affected library. That is all without using the remote library cache feature where you can save compiled libraries to the cloud such that a user only builds the libraries they are changing ever.