Celeste is $2 right now, I got it for free on the Epic Games store but I got it again for the steam cloud saves.
I got Doom Eternal and started playing that, it's actually really good. I feel like I'm pretty bad at it but that means lots of room for improvement.
Of course Terraria is a must-buy if you don't have it already. Same with Portal and such. Stardew Valley is also really good, but I didn't really enjoy it until I played multiplayer with my friends.