Is there a mod which makes it so you can not progress past x level in a career without have the degree for it?

It's a little more comprehensive than the specific feature you're looking for, but if you're interested in such a thing you might like this mod anyway.

Job Overhaul by gamefreak130

The primary features of this mod are making job searching more realistic. Job interviews, more realistic promotions, etc. Careers requiring degrees is one of the settings you can tweak in the mod's options, and it even works with custom careers.

Other than that, I don't know of any others that handle that specific feature alone. But the mod I linked is very customizable and I can wholly recommend it if you like that sort of gameplay.

The above can also be arranged by way of NRaas StoryProgression and castes, but it's admittedly not the easiest thing to set up properly.

Thank you both :>