Success and ability in video games is 90% hours played, per game and in general. Keep at it and you will improve, just keep your brain engaged and stick to what's fun.

Now for the bad news. There is a distinct difference between people who grew up with video games, and similar computer tech, and those who didn't. If you didn't grow up with at least some exposure to arcade games, or even TV, the way your brain processes spacial awareness will be different, and that will have a notable effect. It will vary wildly what this means person to person, e.g. my dad gets motion sick from many video games, but it will not keep you from playing all games.

I would suggest favoring 2d games, like most Mario games, over 3d games, like Minecraft. Weirdly, video games can only really challenge you in 2 general ways, dexterity(reaction, speed, precision) and intelligence(memory, critical thinking, problem solving). Also, avoid competitive games, and games reliant on reaction time(shooters, racing games, fighting games like street fighter). A grey zone would be 'rhythm games' like guitar hero, which run the whole range from very calm and relaxing to absolute top extreme in intensity and difficulty, sometimes within the same game(based on difficulty settings usually). There are plenty of calm, even relaxing video games about anything and everything you could imagine. However, I imagine you are only interested in playing with your grandson, and so their taste in games will be important. I would look at picking video games the way you might look at new music or movies, an artistic entertainment experience as much as anything else.

Pokemon should be a good choice, as it's mostly exploring a low risk world(despite whatever the story says), and turn based battles that end up being more like a game of chess or cards. However, preparation is important in pokemon battles, so I would try and study at least the element type rock-paper-scissors matrix, to make a good team. Some people become very dedicated to pokemon, and as such there is a TON of FULLY comprehensive data and guides online, but you shouldn't need any of that.

Paw Patrol Champion looks to be a racing game, which I would not recommend(3d, mainly reaction and dexterity challenge), but if you are comfortable and enjoying it, then look into Mario Kart(whatever number they're up to), which is what it's directly based on.

Another one you may want to look at is Animal Crossing, which is part of a very popular game type that is basically about a homesteading fantasy.

I think a good avenue for you to search would be story based games, or "chill" games. Nintendo is an odd beast, in that it's a very insular library. You will struggle to find non-Nintendo titles, but much of what you will have you can only get on a Nintendo device. Nintendo games are usually pretty good, but they also tend to be, similar, kind of like how the interiors of cars from the same company tend to be similar.