That's a good start. Also, include him in your own PC activities (some of them, make some up if you don't have anything that he can be involved in at the time), like "I need to find a cool new background, I was thinking this and this might be cool, could you help me find something online?". It gives kids a sense of being useful and wanted, plus a pat on the back, high 5 or something like that when the task is done. And it might inspire him to look for his own background, something he identifies with 😉.

Have a lot smaller kid, he's 4, but this is just something from the top of my head... or how I would play it.

All too much of OS config, IT work, and troubleshooting is a combination of reading docs, trying things, and plenty of online searches. The big missing piece is motivation. That's why I learned as a kid. It was all about building systems to play games.

For your kids, a combination of showing the basics, how to find out how to fix things, giving them agency to modify the OS (assume you'll need to reinstall sometime), and a purpose could get them going. Not everyone find the motivation and interest, but kids are often more able to invest and explore than we give them credit for. I found my son (at age 13) at installed the proprietary NVidia driver for his laptop without my knowing. He just started following tutorials until it worked. Proud dad moment, time for ice cream, and then he went back to playing games with his buddies.