Signal's official Android app does not support being linked, only the iOS and desktop apps support that. This is why I use Molly.

I would ideally want to not have one device being the master and the rest linked to it (e.g. Element can do that for Matrix) but that might be a too big change. And as far as I know Molly does not try to solve that.

I just saw a blog post they’re working on this in the official app, though! Finally. Fingers crossed.