Earlier quoted context omitted.
When did you last try it? Startup speed of Signal-Desktop has been much improved in recent months, like, by an order of magnitude. Maybe give it another shot.
It opens pretty quickly for me, but almost every time it wants to be re-linked to a mobile device. Signal is really annoying with all the things it wants me to do. Re-linking a mobile device. Re-entering a PIN/password for no reason other than to prove that I still know the password. And when I'm finally logged in it shows me a completely useless selection of mostly obsolete contacts.
You can turn off the PIN reminders in Settings → Privacy.