I was disappointed in Everybody 1-2-Switch because there was no option for single player mode.
Lovers in a strange space time
I know Super Mario Party allows for single player. Not positive on Mario Party Superstars since I’ve never tried it single player but I would be quite surprised if single player isn’t supported on that. That said, my go-to party game is actually Smash Bros. Ultimate and that definitely supports single player.
Mario Party Superstars has a single player mode too as well as 4 person co-op both online and offline.
Mario kart?
Smash
WarioWare.
Stardew Valley, most Lego games, hmmm… Luigi’s mansion 2, Super Mario 3D world, Super Mary Odyssey, Pikmin 3, KeyWe and maybe Children of Mortia? We play a lot of cozy games and those are our favorites