I’m currently working on a future secret Field Guide project that involves a lot of writing. So, before digging in I took another look at all the writing tools, as you do, and settled on Ulysses(https://ulysses.app). That was in January. The Ulysses updates this year have only affirmed that decision.
Most recently, we got version 21 on the iPad and iPhone(https://ulysses.app/releases/). The headline feature is grammar, style check, and text revisions. With revisions mode, you can track your annotations and comments in addition to the app’s grammar and style suggestions. I immediately implemented these features in my secret project, and my words are better for it.