Any idea about how the security posture changes? I would expect some significant tradeoffs are required to make all your messages appear in your browser
I haven't used it in a while but I think it's probably similar to WhatsApp where it basically just tunnels it through your phone without actually running a Signal client on your machine.
It's not, once linked the desktop client can be used independently of your phone.
i'm not 100% sure how it works, but it seems to sync some messages. Not working perfectly as my desktop client does not have the full history from a chat, even though my phone does. It only has some of the messages from where the desktop client was first started.