Other than the FairPhone, which you already mentioned, nothing really matches all criteria.
I’d give a nod to the Pixel line, though. Google already offers 5 years of software updates, and the next line is rumoured to get 7. Plus Google allows Custom ROM support, which makes it a fan favourite in the privacy community. Granted it’s not as repairable as the FairPhone, and it’s not as eco-friendly, but it’s decent enough.
A TV will do, for a child. He doesn’t NEED anything fancy. Will it be a great experience? Absolutely not. Others here have already gone over the issues. That being said, if cash flow is an issue (relatable), it’ll be fine. Console gamers have been doing it for literal decades. I also used to do it, back when I was a kid, when we had an old 480i TV. Your kid should be grateful that he can play his games. People can spend too much time worrying about not getting the best experience (especially when giving advice to others), when it’s often not needed.
Best advice I can give folks is not to be afraid of haggling your contracts. When their introductory offers, and the initial contract ends, call them. Though, it would help if there is actual market competition… though from what I hear about the US… that’s non-existent, when it comes to broadband packages.
I can see the appeal. Of course it would be easier for the average user, for Steam integration (eg: with Steam Deck), but the real killer feature would be cloud save syncing. Add in the Community features, like forums (good resource), and the potential for guides, on getting settings optimized for a game.
Having it open source, does not make it good. I think I’d prioritise making it fun, try to.make a profit, and then open sourcing it. I don’t think having it open source will help you sell copies… you might sell less. Make your money first, have a feasible business strategy, so you don’t go bust. Then try to keep the game alive vis open sourcing it.