You can dock the Stem Deck using a USB-C hub to connect to a monitor, keyboard and mouse. This is a use case that is supported by Valve and Valve sells a first party docking station to facilitate this.
There have been multiple people citing on the Steam Deck subreddit that they regularly use the Steam Deck in this way and a few even saying they use it as their daily driver.
It's a laptop in a handheld form factor. That is all.
I think the first thing to note is going back to my OP in that I simply don't understand why people like yourself will go to such lengths to argue against Linux desktop, citing all the issues you've had with it when I don't see this kind of kick back against any other technology or even any other concept more widely. If people don't like something or don't think it'll work they'll either ignore the thread or post a much shorter response expressing doubts. I think the only thing that I saw get to a similar stage was crypto, but it seems like the crypto community split off into their own little world whereas the Linux communities still stay in a fairly close orbit to technical circles.
I think secondly this speaks to another comment I made elsewhere where the counter-arguments for Linux desktop are firmly rooted in personal experience. Here you're also explicitly saying that the issues you're having you don't think are going to improve.
But Linux had improved. It's improved massively in the last 5-10 years. 2 years ago I couldn't play Apex Legends. 5 years ago I couldn't play Direct X games without a lot of effort. 10 years ago I couldn't get YouTube or Netflix.
Things are improving and whilst your personal opinion may still be that Linux still won't be viable, the sheer number of people that comment in a similar vain means that there is a negative smog around Linux that stops or discourages more positive discussion.
So I'm not against Linux desktop - I'm just saying the people singing it's praises probably have different expectations from me so I'm trying to add another viewpoint (because it's always subjective experiences in these threads - I can't remember reading statistics about hardware coverage and similar news)
Linux on the desktop usually means a Windows replacement - historically, and the most relevant meaning to me personally.
The reason I'm not hopeful things will improve is same as always - not enough critical mass to get the momentum going. I was buying a PCIe wifi card a few months ago and wanted to check support for Linux in case I try again. There were zero options locally where I could reliably determine that onboard BT would work, and there were like 5 modern cards available.
I just don't see what commercial entity is going to push Linux desktop development ? Linux server is mostly a result of big players working together to commoditize the OS, scaling with commercial os on the backed would get prohibitively expensive immediately. Don't see where the desktop push will come from.