The only mobile game I’ve spent any amount of time with was You Must Build a Boat. It’s a bejeweled clone with dungeon crawling and RPG elements. It’s dirt cheap and has no ads or in-app transactions. I wouldn’t have it any other way.

I really like Data Wing. Cool top-down 2D arcade racing game with a cool story, free with no ads. It’s obvious a heap of passion was poured into the game. Still my favourite mobile game.

EDIT: I use Android so I’m not sure it’s on the Apple Appstore but I don’t see why it wouldn’t be

Osmos is a wonderful meditative game on iPad.

Stardew Valley. Loved to play it on long haul flights, doesn’t need Internet.

Slay the Spire has a decent iOS port

20 minutes till dawn. You kill stuff and build around your character trying to survive for 20 minutes.

mindustry is my fav

it’s a crazy good combo of resource management, tower defense, rts, and sandbox creativity

added bonus that it’s open source and even has multi-player

Worldbox, if you’re into world-building and minimalist pixel art.

Dead Cells! Best mobile port of a PC/Console game I’ve ever encountered.

Juno new origins is a good game, just make sure your ipad doesn’t light on fire

Pathos - Nethack Codex, a very playable traditional roguelike based on Nethack.

Unciv, an open-source Civilization V remake.

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Currently on my phone:

Civilization VI Civilization Revolutions 2 Into The Breach Mini Motorways Shovel Knight Dig Slay the Spire Grindstone

Legends of Runtera. Probably the most user friendly free to play card game. You don’t buy booster packs, you buy the cards you want directly and can get enough recourses by simply playing often.

FTL plays great on the iPad