When I was a kid, I got the game Set as a gift. I could never find anyone to play with me because I was too good at it, which sounds braggy but is true. Ask my parents.
Anyway, Set is a relatively simple card game that involves looking for “sets” of three cards. Each card has one, two, or three items on it, shaped like either an oval, diamond, or squiggle. Shapes are solid, shaded, or outlined, and purple, red, or green. You want to find three cards where each component is either the same for all three or different for all three.

See how the highlighted cards have the same number and shape, but different color and shading? They make a set. You and the other players are trying to see who can find the most sets the fastest.
Self-plug moment: I like that the version I created does not automatically keep score, so you could approach the activity as a cooperative puzzle, working together to find the most sets. It is also non-directive due to the PlayingCards.IO platform if that fits your therapeutic approach.
That being said, maybe you want to keep score but you don’t want to take your attention away from the session. Maybe you want your client to practice working within rules enforced by a platform. If this is you, Buddy Board Games has you covered. Simply create a room and have your client join with your private link. It also has a function to give you a hint if you get stuck!
If you and/or your clients like brain games and puzzles, this can help flex their focus and problem solving muscles. I even play it by myself sometimes when I need a break.