What kind of stuff is he into? My son loves simulator games like…

• BeamNG Drive - better with a wheel but very playable on controller.
• Snowrunner
• American truck simulator
• Farming simulator
• Construction simulator
• Lawn mowing simulator

There are a lot of good kart games on PC also, though I will say that my favorite - Sonic Racing Transformed - is much harder than Mario Kart.

Minecraft Dungeons is basically Diablo for kids.

Minecraft is good but I also like Dragon Quest Builders.