Fractal does not currently have encryption support, but there is an initiative for it.
We are now partially using matrix-rust-sdk rather than our own implementation. (See #636) and are working towards using it completely.
For Signal see these threads, I don’t know if Signal encrypted calling is working but there are a lot of methods being attempted to use it (Signal) on mobile Linux so it could be buried.
There are more around the forum but these are the two I see most often right now.
Also see Waydroid as a possible alternative, though some users report build issues OK the Librem5: