radodomic Have you tried Molly, a fork of Signal? One of its features is linking Android tablets to your set of connected Signal devices. (Apparently this can work, even if your primary devices uses vanilla Signal and your Android Tablet uses Molly - but double check this.) This was added in September 2023 and was fully bug-free in December 2023.
There is a custom F-Droid repo (more info on that on its GitHub repo) for both versions (non-FOSS and FOSS).
You can download the FOSS version of Molly via Accrescent, which has been mirrored into the GrapheneOS Apps store for at least 1 month now.