Signal Desktop is somewhat buggy, not that full-features, and doesn't integrate that well with the rest of my OS, but otherwise it's working fine, and I can use it simultaneously with my phone. (But I can also use it with my phone turned off, which I love.)
It doesn't work at all for me, because it requires a mobile phone number, which I don't have (a phone + any monthly subscription fee doesn't fit in a tiny fixed income budget).
On a desktop app, it's not reasonable to ask for a phone number. Ask for something else; email, for example.
Of course many don't want to tie their communications to some other identifier and that's fine but that does mean that Signal isn't for those people.
Is that perfect? No, but if you want another unambiguous identifier, it's going to cost. Moxie does not have a lever that can move the world; if you think you do, you are probably well invited to haul on it.
Nonsense - my XMPP addresses are free, globally unambiguous, federated, and support 3 types of end-to-end encryption. A phone number is patently unnecessary. The only reason to require a phone number is to tie the encrypted packets to a known identity.