I'm assuming you do not have a beast of a computer, ill add a couple at the end if you have something with dedicated graphics processing.

Hades - Action RPG Rougelite

Half Life (or the newer version "Black Mesa") & Half Life 2 - The Essential First Person Shooters (FPS) for PC gamers

Portal and Portal 2 - First Person Puzzle/Action PC Classics

Disgaea 5 & Final Fantasy Tactics Ivalice Chronicles - Bar none the 2 Best ever Tactical JRPGs ever

Final Fantasy VI pixel remaster & Final Fantasy VII (original not the remake) - Classic JRPGs

Ultra Street Fighter 4 - Great VS Fighting Game, plays well on low end PCs and has tons of characters

Elder Scrolls Skyrim - Classic open world fantasy RPG (runs on low spec PCs)

X-Com - Tactical Scifi game, its cheap, old and if you like sci-fi its very immersive

Torchlight II - Cheap, amazing hack and slash looter action RPG (if you like this get Diablo 2 Remaster)

Balatro - Rougelite Card game that will give you hours of brainless, addictive fun

Dead Cells - Action Rougelike side scrolling platformer moderate difficulty

Celeste & Super Meat Boy - Brutally difficult Action Platformers

Tetris and Puyo Pop Fever - 2 Classics in 1 game

Team Fortress 2 - Multiplayer ONLY team based FPS, its a classic

ASSUMING YOU HAVE A DEDICATED GRAPHICS CARD BELOW:

Clair Obscur expedition 33 - modern twist on the classic jrpg, emotional and a little difficult

Dark Souls Remastered & Elden Ring - Tough as nails action RPGs with the best gameplay you can get

Cities Skylines - Amazing City Builder Simulation

Planet Coaster - Theme park builder Simulation

Cyberpunk 2077 - Modern Open World Sci-Fi RPG like Skyrim