You can invite someone to Signal using the "Invite Friends" menu in the app, which will send a text message or email.

You can archive chats in the Signal messaging app to hide them from view if you don't need them clogging up your inbox anymore.

Instead, you need to open and register Signal on the new phone and select an iOS transfer. Then you use a QR code to connect the old and new iPhones and a transfer will begin. Be warned — that ...