I’m writing a new book (suscribe to get the rules to survive freelancing first) and using Scrivener as always, but it’s pretty rough on iPadOS. I’ve looked at Ulysses as well, and in my looking found this great post from Matt Gemmel on using Ulysses to write his books.
The truth for me is that I don’t love any of the writing apps on iPadOS currently. A bunch work, and I like features of each. I wish I could program Swift (or had the time to learn it) and then I’d work on building one that I could use for everything.