@ohmu
I think @AllKeysGDS mentioned all of them but i can give a little context.
Haven was FANTASTIC as a couch co-op adventure game about two twentysomething lovers who've fled to an abandoned planet. Great dialogue. Highly recommend.
Resident Evil 5 (Chris & Sheva) has built in co-op and it's fun if a little clunky
It's been a few years but we also loved playing through the Halo Master Chief collection as she said.
River City Girls 1 & 2 are hilarious side scrolling beat em ups with cheeky humor, excellent art, and very fun, engaging combat.
Streets of Rage is similar but definitely less funny and more combat focused
Cat Quest 2 specifically let's P2 play as a dog, which i appreciated.
Guacamelee was a 2 player metroidvania we liked as well.
On the lighter side, Overcooked, Lovers In A Dangerous Spacetime, and Out of Space are all fun without complicated controls or a deep story. Easy reccs
All of those have real built in couch co-op.
We got good mileage out of Remnant 2 and Outriders, but neither had couch co-op so we had to use the two screen method. Halo Infinite was the same way.
We gave IT2 a shot but bounced off it halfway through for reasons i no longer remember.