This has always been a game that I thought about playing way back when it was popular (and when the smash styled fighting game Fraymakers made it relevant again), but I don't have the finances to get it. You're going to see this constantly for these games, but maybe someday I will get them if I do.
VVVVV is 5 bucks full price and regularly goes on sale for 1.24 euro. But I get it...it used to be in every humble bundle back in the days.
Anyway...some other gems I've found (not gonna list price on everything, though)
Love eternal. Tough-as-nails one-screen platforms you just WANT to beat (it reminds me of celeste in that way) with jumping and VVVVV-like gravity shifting. Very weird storyline that I can't decide is either random or deep on a level I can't comprehend.
Mina the hollower: this is like a gameboy color platformer style game with winks to the old Zelda games. This is probably known since it's made by the shovel knight crew.
Pipistrello and the cursed yoyo: in the style of the gameboy advance. Less known (I think), but I like this one better. It captures the more quirky and loosey nature of those games.
Nurikabe world: recommended it elsewhere and I think
@hippy dave got it because of it. Anyway...this is a chill "connect the ponds" pure puzzle game. By the numbers, but: BUTLOADS of levels, good visuals, great handling, and a good difficulty progression
Froggy hates snow: saw it, pirated it...and then bought it. This is full on casual game: you start in a warm tent in the snow, and need to get in the snow to dig it flat. Collect resources, upgrade your abilities, collect keys, defeat waves of enemies, and finally unlock extra powers. It's somewhat roguelike-ish (and, granted, repetitive if you keep playing), but it's so casual that it's better to just see it as individual games.
(Wilmot works it out). this is the cosiest of cosy games I think I've ever played. You're a smiling square who has an abonnement on a puzzle magazine. Meaning: for every jigsaw puzzle you complete, the postman brings more. If you've played Wilmot's warehouse, you know the controls. It's fun, it's chill...but those puzzles get downright unfair somewhere down the line.
Cairn: i'm not sure how many mountain climbing games there are, but this one takes a strong contender in being the best one. Think CLOP or octodad, but instead of a silly slapstick game, you have to carefully position your hands and legs on rocks in order to secure yourself. And I have to say: this game makes me scared of heights (note: unlike the previous entries, you need more than a potato PC to run this thing)