A European alternative would be excellent (I'm in the UK), but no such thing exists, that said, Signal's server and clients are open-source and can be self-hosted, or even deployed at scale by a European government/entity if they so wish.
I work in the "secure comms" space, and I have reviewed every line of code in the open-source server (as of the revision I last worked on), and built products on it, and though I can't prove they run the same code they publish, I'm "happy enough" with what I see that I'd use it over anything owned by Meta any day.
In an ideal world, I'd host it myself for everyone I communicate with to use, but without federation that's not a possibility, so given a choice between Signal and WhatsApp, the decision is hands-down Signal.
