While not designed with D&D or role-playing games specifically in mind, Ulysses is definitely worth mentioning when it comes to your DM’s Binder. At it’s core it is a markdown app for writing and note-taking and while this may not appeal to some, consider that as a Dungeon Master you’ll potentially have amassed hundreds of pages of text over the years.
Now of course you may have put all your hard work into various other apps or web services but where Ulysses shines is it’s lightning fast, tag-able and searchable sheets. This means wether looking up a non-player characters, magic items, custom encounter tables or anything else you put into it - it’ll come up quick and painless. I have literally hundreds of pages of text I’ve thrown into the app and it is by far the fastest, most solid app I’ve used.
What’s more is you can have multiple windows open on PadOS which means on the left side you might have your adventure notes and on the right, perhaps an NPC or a magic item. For the past two years I’ve had Ulysses along with in-game music and occasionally Encounter+ (another app) all running on my iPad Pro (2018) without ever worrying about battery power over 7+ hours of game play. Worth looking into if you’ve not tried it!