I cannot fathom the proliferation of phone-only messaging apps.

Am I really the only person who prefers to type on a full-sized keyboard, and see my multiple conversations on 27" screen, as opposed to one and a half inches of no-feedback glass surface? :-/

I went to Signal site, downloaded the Windows app, and once installed, it asks me to link my phone. No option for any other signup. NOwhere in the download process or on main site does it warn me that this is a phone-only app. The desktop app itself simply starts to a "Connect your phone" screen with no explanation why I have to do it, whether there are or aren't alternatives, etc. Nothing about this is remotely user friendly.

I have half a dozen laptops, two phones, few tables at home alone; the notion that I must be crippled to only communicate via the smallest, least practical communication device I own; and then be horribly crippled in attaching one-at-a-time additional device but with crippling dependency on said phone... I guess I'm a negative focus group and completely out of touch with the realities of the world, but I cannot imagine or understand who wants to live like that :-/

I don't understand your point. You have full-size keyboard access through Signal's desktop app on your laptops paired to your phone so what's the problem?
Can I use Signal from desktop only? Can I create an account from desktop? Is my account independent of any specific device? Can I use Signal on multiple computers at the same time with correct credentials?
> Can I use Signal from desktop only?

Yes, the desktop client functions independently from the phone client once linked (so not like whatsapp that proxies everything through your phone).

> Can I create an account from desktop?

Technically yes, but you either need to compile the desktop client yourself[0] and miss some features or use something like signal-cli[1] to act as the main client. So it's not supported (yet?).

> Is my account independent of any specific device?

The first client that registers acts as the main client, so no. But it might get easier to restore access on a different device without using backups with the secure value recovery[2] stuff they are working on.

> Can I use Signal on multiple computers at the same time with correct credentials?

It's possible to link and use several desktop clients at the same time.

[0] https://github.com/signalapp/Signal-Desktop/blob/development...

[1] https://github.com/AsamK/signal-cli

[2] https://signal.org/blog/secure-value-recovery/