This is counter-cultural advice, to be sure.
I base it on what I've seen in my own children. Video games displace important things in a kid's life:
They lose the ability to persist at a difficult task
Most tasks in video games aren't that difficult. Even considering a game like Minecraft or Stardew Valley or Factorio where there's a lot of building or working out complex systems, it's a very different thing from being persistent at a real-life skill.
A real-life skill, like drawing or woodworking or playing the piano, doesn't usually give instant feedback. Video games make things easy, and they also nearly always make it clear whether you're doing the right thing. This blunts the ability in real life to keep at something when the feedback isn't always clear, or may not even exist.
It's similar to the contrast between learning a language by talking to people and learning a language with something like Duolingo. In real life the feedback is messier, and can seem not worth the effort compared to a prepackaged language-learning system.
They lose interest in doing other things
I wouldn't say either one of them is hopeless at this point. My daughter (who is 10) in particular spends time on creative tasks; over several days she drew elaborate cards for her elementary school friends who will be at the same school next year (Realschule, here in Germany).
But she did this because she was grounded from the computer for four days. Fortunately she was still able to find a way to entertain herself and was still willing to put forth that kind of effort.
My son, when he's grounded from the computer or simply has exceeded the amount of time we allow him in a single day, can't seem to find anything to do. He lies around bored. Sometimes he reads. But I can already see that his attention span has suffered from years of electronic entertainment. Reading or bicycle riding or drawing (which he used to enjoy) don't hold his interest by comparison. (Honestly, I can see it in myself, too. I can only sit and read for so long before I feel that "itch" to grab my phone or go sit in front of my PC.)
Maybe you're going to do it anyway, though
In that case, spend some time thinking of some firm rules. Here's one you might try: No video games unless you play them together. This keeps video games a social activity, and hopefully keeps the time fairly limited. It encourages choosing games that are pleasant to play together, and gives you veto power over games (though hopefully you'd have that anyway). It also lets you closely observe the effect games have on your son so you can shut down problematic ones that encourage rudeness, addiction, and other undesirable behaviors.