Unfortunately the Signal recommended by many people may not work for you, it cannot work on multiple mobile devices at the same time, for example on a smartphone and tablet.
I don’t understand why no one recommends Jami? It’s the only messenger that works without a server at all. And yes, it has the ability to forward messages to itself (to use as a note) and works on any devices at the same time.
Open Signal rewiews on GooglePlay, there’s every third review about this situation. I forgot to mention, i’m talking about the Android version. The ios version works on ipad at the same time