Let's list some great mobile games. Preferably ones you can pay for once and be done, or free ones that have microtransactions that you don't need to do to just play the game (e.g. Marvel Snap). Leave out pay for power or games that have "charges" to stop you from playing until you buy more or burn time.

Edit: Thank you everyone for your suggestions! I compiled a list here that is, I believe, mostly Android. If you're looking for iOS only suggestions it looks like Apple Arcade was recommended regularly and also user Recognition101 had a comprehensive list I will refer you to: https://recognition101.github.io/ios-games/

Here is the Android Games List:
-Square Enix re-releases
-Stardew Valley
-Monster Hunter Stories
-Disgaea series remakes
-Vampire Survivors
-Slay the Spire
-Shattered Pixel Dungeon
-Slice and Dice
-Bloons series
-Sproggiwood
-Pysol FC
-Lexica
-Mindustry
-Overboard
-Old PC Game ports like Baldur's Gate 1 & 2, SW:KOTR 1 & 2
-Hoplite
-Simon Tatham's Puzzles
-Rogue Adventure
-Cultist Simulator
-Mini-Metro
-Wordament
-Retro Bowl
-Antiyoy
-Marvel Snap
-Star Realms
-Wingspan
-Team Fight Tactics
-Battle for Polytopia
-Where's My Water?
-Underhand
-Badland
-Eat Me Please
-Z Origins
-Yellow
-Dawncaster
-Ollie's Arcade
-Orna
-Night of the Full Moon
-A Dark Room
-The Ensign
-Universal Paperclips
-Opus: Rocket of whispers
-Opus: The day we found Earth
-TerraGenesis - Space Settlers
-Sheltered
-Seedship
-Framed
-Plague Inc.
-Gravity Defied
-Magic Research
-Star Wars Galaxy of Heroes
-Peglin
-Civilization series
-Rebel Inc.
-Boom Beach
-Professor Layton Series
-Slay
-Ritual

I play a good deal of Simon Tatham's puzzles (iOS version) and Ordinary Puzzles (which is only one type.)

I've spent a good portion of the night trying to find some other open source / free / no IAP puzzle games, but for the most part I've come up empty.

Anybody know of some treasures out there?