Games

Since you played all Borderlands and just finished a D&D game, why not play "B&B" on Borderlands, there's a game called Tiny Tina's Wonderland which plays like Borderlands but is set in "medieval" fantasy (but still has gun for some reason)

Cat quest 2 if you like cat puns and something casual. (Cat quest 1 is single player and doesn't (really) connect to the storyline of the sequel)

Serious Sam - almost any version!

Ark survival evolved is something my husband and I enjoy playing together that's quite fun. The base building and dino taming together is very enjoyable if you're on a private server.

If you give this one a try, make sure whoever is hosting sets their server to private and invites the other person via steam. Otherwise you might get randos.

The Division 2 is fantastic co-op and often gets put on sale.

It's a very different experience, but have you considered Baldur's Gate 2?

Dark Souls 1 (remastered) & 3 along with Bloodborne are good options.

Wildermyth is an awesome indie RPG that I've had a lot of fun with as a two-player coop game. It's a turn-based dungeon crawler with a strong focus on role play and party dynamics.

I hear great praise for Across the Obelisk as a coop game from my friends, although I personally bounced off of it. It's a roguelite deck builder like Slay the Spire, but with multi-player, lots of meta progression, and a heftier time commitment for each run.

Gunfire Reborn is a roguelite looter shooter that's a blast in coop. I think it's still in Early Access, but what's already there is enough for me to be happy with it as a full game. To me it's a spiritual successor to Borderlands in combat and gamefeel, but without the grinding.

Unraveled 2 is a beautiful and fun game for 2 people.

You should try a wholesome cute game called Bread and Fred!!! It's got penguins!

It's an old game, but Pixel Junk: Monsters is a ton of fun as a co-op tower defense. Don't bother with the sequel - s'bad.

BattleZone (the one from like 2016) is surprisingly fun and has optional VR support

Not played most of the games you mentioned so not sure this'll be your thing, but I've gotten back in to Sky: Children of the Light recently and it's been great.

It's beautiful, f2p (ad free!!!) on a bunch of different platforms, and going in as a pair will give you a head start since it has a social aspect and is designed to occasionally get players to cooperate (though you can play alone just fine, I do most of the time and cooperate with and befriend other platers). It's mostly chill and you can take it at your own pace and make what you want of the world - follow the spirit guides and play through "proper" or fly/run/swim around and discover things on your own. You can use skills like playing instruments and taking photos, decorate your own or shared spaces, customise your character, chat to people from all over, or just chill in your favourite spot.

I couldn't find it mentioned already, but I really loved Vagante. https://store.steampowered.com/app/323220/Vagante/

Since you mentioned Vintage Story I'm gonna go ahead and praise that suggestion. A game truly worth supporting! Developed by only two people, with a huge dedication. Game has a lovely community too. Definitely give it a shot 👌

Here's a co-op indie game I made for Windows PCs. $1.

https://www.cheerandtrack.com

Prodeus is still EA, but it has a solid first episode with good Co-op gameplay if you're into retro style shooters.

If you really want to go old school, OG Doom from 1993 and Bungie's Marathon Trilogy(1994-96) support co-op. I haven't tried Doom yet, but you do need to be technical to figure out Marathon co-op.

Remnant 2 is sweet!

Outriders. And a bit more tame but Unravel 2 for in-person.

Abiotic Factor. It's basically a co-op Half-life.