Ended up with 2023b for other MATLAB things and 2023a for MATLAB with cvx. Perhaps I could have gone with 2023b for both, but didn’t want to risk it 
I followed this post to get cvx up and running:
Installing CVX on a new Mac
For anyone finding this post later on, you have to do the “repeat” process for like 10-15 times, so hang in there. It’s worth it!