I've upgraded a considerably big Angular NX monorepo more than once (we started on version 7 and now are on v15). No argue it's not easy, but about the "too many files updated' most of the times they were indentation changes. Other changes involved adding a { static: true} to the ViewChilds but that happened only once. Last updates were not as flawless as the team expected, bit this was due to old unsupported libraries being used, not because of our code.

Do your particular "too many changes", go far further than an indentation change on most files?