I've recently bought a 12.9 iPad pro and have struggled to find a good use case. For me, a kindle is better for books, paper and pen is better for notes, and a computer is better productivity.
Back when I was flying at least 3x per month, my iPad was perfect for staying on top of emails and Slack messages while in the air. Cramped seats and poor wifi are not conducive to laptops, even my 13" MBP. It also helped me focus bc it prevented me from falling into the trap of having a dozen tabs open. I have not found much use for it since COVID.
Displaying sheet music while I play the piano. And before that, nothing. I only have an iPad because I needed it to demo the app I was working on at the time.