Realistically, the majority of people will not switch to threema @ €5.99. It's already extremely difficult to get people to leave WhatsApp. They're not going to pay for it.
https://european-alternatives.eu/category/instant-messaging-apps
Signal isn't EU based, but afaik not profiteering or harvesting data.
EDIT:
There are quite a few EU based according to this.
https://alternativeto.net/software/facebook-messenger/?origin=eu
Probably best for all of us if nobody can ever have nuclear weapons, but what do i know..