Portal 2 was my first thought as well. It can also work as a good litmus test for how they will respond to FPS controls. You can try kb/m or controller and see what feels natural. My partner (we found playing left4dead after portal) is an inverted controller person. Which was wild to me considering they worked in a heavy clerical field and really took to building keyboard with me. Yet, no kb/m for gaming. After that switch , they were able to enjoy co-op 1st person stuff a lot easier.
After portal we played borderlands 2 together. It’s low pressure most of the time and can be a background activity while you talk and hang out. The story is kinda cheesy but it’s fun to share the inside jokes with someone and bonded us in an unexpected way.
Hopefully those work for you!
Edit: it takes two and split fiction are really fantastic coop experiences as well. But, it take two should probably have a small warning for emotional content. Split fiction is a ton of fun but does get kinda difficult for less seasoned players. I found it endearing helping through those sections, but it could be harder for others. There are some moments that we both audibly wowed at though! That made the difficulty worth it.
I tried going back to it on pc recently and was met with a pretty janky experience. GoG and Steam versions. I ended up emulating the PS2 version with some upscaling and it was great. There’s community texture packs and widescreen patches as well if you have the hardware to run them (low bar fwiw, I had success with an anbernic android device and a few mods as an example).