I’d just like to point out that if Signal leaves the EU, it will most likely just mean that it’s not available through the official app stores. With Signal updating itself, it’s just a little inconvenient to install it on a new device, though, they even said that they’ll try to make it as easy as possible.
Well, eIDAS is already on its way. Not sure if I understand correctly, but seems like they’re trying to seize control over server<>client encryption.