Hell Let Loose has a Free Weekend till the 29th for anyone that is disappointed with recent Battlefield titles or wants to try a Multiplayer/Squad based WW2 game, if in doubt download and try it out for a bit:
Civ VI also got a Free Weekend:
Also the "Remote Play Together" Sale is on for anyone who hasn't noticed:
https://store.steampowered.com/sale/together
There's some cool older CoOp titles at lowered prices, a lot of which also don't even require Remote Play like Magicka, Castle Crashers, Broforce, FORCED, the Trine games etc.
Streets of Rage 4 is part of the Sale and afaik the lowest it's been so far, one annoying peculiarity about it though is that it supports 4 people Couch CoOp locally or if you're using Remote Play, but only 2 for Online CoOp where people play their own versions and start a game together:
Anyone got any recommendations for good CoOp titles (gems I might've missed in a river of shit)?