I'm confused by your post. I use signal seamlessly between my desktop, iphone, and ipad using the same account. I can take photos with my phone, post them to a chat, then go back to my desktop to type longer messages more easily.
Is your problem that a phone is required to be the primary device when doing this?
Then you clearly haven't read my post thoroughly. I repeatedly mentioned my issues being with Signal not allowing multiple instances on Android devices using the same account, while you're talking about Signal on Apple devices.
Is your problem that a phone is required to be the primary device when doing this?