School mods that add university classes to high school?

KawaiiStacie still has a school mod: https://www.kawaiistaciemods.com/post/better-schools-mod

I don't know of any that do what your header asks.

Try this one :D

https://www.patreon.com/posts/university-teens-31714934

If you want a higher chance just edit the mod in Sims 4 Studio, there's a variable in there that asks what percentage and it's set to 5 from memory I set it to 50.