I'm sorry, but I think we have a mismatch on our understanding of the word proprietary. A desktop PC has some proprietary things, firmware, and the likes are almost always proprietary, as in they're the propriety of the company that made it, which means that if someone else tried to make them they'll get sued. But most of the schematics and connectors are an open source standard. Which means that if something breaks, you can buy a replacement from a different company and everything should work.

Laptops are mostly the same as well, in fact they use much of the same standards, the thing is that the form factor makes it difficult for third-parties to make the pieces, but they exist, and are legal.

A company can charge as much or as little as they want to fix their device, that has no impact in whether the device is proprietary or not. If you are legally allowed to open, repair it and change parts with third-party ones it's not proprietary. If anything in that chain breaks, e.g. you're not allowed to open or repair, or third-parties are not allowed to make replacements then it's proprietary.

Besides having made a device that's essentially as proprietary as a desktop (which is to say almost no proprietary at all), Valve is also offering their own replacement parts and cheap repairs, which are all things to commend, but if Nintendo did it for the switch the switch would still be proprietary.

Most of what you mentioned is right to repair, which is important and all the more reason the Deck should be praised, but it's not what proprietary means.