Tou can try borderlands games, all have a campaign that can be played with up to 4 players in coop.
Also you can try "A way out". It's a game designed woth coop in mind.
If you like these type of games you can also play diablo 3 in coop, or some alternatives like this one: Torchlight series, path of exile, i think van helsing games also have coop.
You can also play destiny 2 online with a friend. Warframe would be another similar game with this one. The division 1 and 2, should offer a similar setup. You have to complete online missions.
Gears of war series, you can find the first gears of war game on PC, and gears of war 4 and 5. The second and third game i don't think were ported to PC. I know they are available on windows 10 store, i didn't checked if they can be found on steam too.
Dying light and dead island games, the campaign can be fully played in coop.
Portal 2 has a special coop campaign, is kind of short but it's fun to play.