Monument Valley and Gorogoa are both excellent and free of nonsense.

Both are available on mobile and Steam. Gorogoa also on GOG currently 70% off.

Meant to link monument valley 2: https://www.monumentvalleygame.com/mv2

Sparklite, I don't know what it looks like purchases-wise, it was free with gamepass and had no in-app purchases when acquired that way. It's probably one of the newest games I'll post about. New enough that it was possible to get it with gamepass, lol. The game sort of has a modern retro zelda feel. I don't think it's a particularly long game, but it's certainly enjoyable and pretty casual. I think if it has transactions, reading other reviews it might be like a "purchase the rest of the game" style thing. So basically a free demo that you can then choose if you like the game enough to pay.

Imagzle. There are "buy more levels" but there are plenty on the main one. It gives a picture, more or less, abstractly related to something. Art, movie, book, many random things

Potion Permit is about $7, but pretty fun. If you got $10 to spare, Ex Astris is a jrpg that's pretty good.

Emulation!

Cosmic Combo, an iOS port of Johan Peitz’ PICO-8 game Cosmic Collapse, is good.

2048 but a version from F-Droid: https://f-droid.org/packages/org.secuso.privacyfriendly2048/

I played a cool one called Pirate solitaire, very charming

I've been addicted to Simon Tatham Puzzle Collection recently, it's very fun. For example pegs puzzle, I have not yet found a solution

Old School RuneScape potentially fits this description

Walk master

Pixel dungeon, but it's not really low stress.

You can get a port of space cadet pinball from GitHub!

Antimatter Dimensions

Wuthering Waves is Hella good. Technically it's an open world gacha game, but I played through all the storyline (the developers will be forever updating the story a la Genshin Impact), and I never spent a dime on it.

Also, I have spent money on Cooking Diary. However, I went about 3 months of daily play before I did, and it was more about me being impatient/telling myself "You got 3 months of daily play, you can drop the devs $4.99". I've played that game just about daily since Memorial Day 2023, and I've dropped $5.00 quarterly. There are regularly moments of infinite lives that exceed an hour or two, that it genuinely isn't necessary. I spend the money more as a "thanks for not making this ducking game contingent on microtransactions, making it good, and maintaining/update it."

Gardenscapes is the original match 3 and build a mansion and is still my favorite. There are micro transactions to get additional power ups, but the fact that they are constantly updating with new seasonal events and you never run out of levels

Out of the Dark is alright.

Gubbins is a fun word game, it's a one time purchase and apparently part of the profits go to charity due to Hank Green investing in it in a creative way.

Star command, anomaly, world of goo, EDGE, knight of pen and paper...

These are some good ones I got from humble bundle over the years but many are quite dated so not sure if they're still around. No BS microtranactions

royal match has no ads at all, its pretty fun just gotta ignore the microtransactions which is pretty easy to do at least compared to other games

2048. Though im sure that one has ads. Probably depends on what you grab from the internet, as usual.

Mobile games suck.

Old school RuneScape, it has free "demo" version which you can easily put a 100+ hours in. And if you really love there is a subscription model that's kinda expensive if you bill monthly, but no other micro transactions.

Oh n0 and Oh h1