Again, no sideloading needed. You're misunderstanding the executive.
They enforce this by freezing bank accounts and issuing fines to corporations, not by internet censorship.
So any company that doesn't have money flowing through the EU is unaffected. And any company that does have money flowing through the EU has a choice to either pull out of the EU or to fuck over their users.
I don't see how this would be a problem either except on Apple. Blocking the sites offering the apk/deb/exe/etc - good luck, doubt their censorship skills are that good given that they're unlikely to want a ton of collateral damage like more authoritarian places.
I'm European using signal, I frequent in two countries very often (not neighbouring countries) and for the past two years I've noticed more and more people using signal.
Ditched whatsapp half a year ago and haven't had problems. Some friends use both signal and whatsapp.
Not saying many in whole Europe use signal but it certainly is not only popular in US.
Edit: but not saying using signal will change anything if this bill passes. No matter what popular app we use we are going to have no privacy at all if this thing passes...
WhatsApp uses the same encryption as Signal and chat screening won't be exclusive to WhatsApp anyway, so whatever WhatsApp will need to implement to comply, Signal will have to follow.
End to end encrypted, I think chat control is all about client-side scanning so the app being open source is a big deal and would prevent client-side scanning because even if they build in client-side scanning, it's open source and people can remove it.
Signal is pretty control freak-y, so would not be surprised if they can somehow prohibit third-party modifications entirely. That would be out-of-character for them, though, so doubt they would actually go through with this.
Still, if that went through, I'd discount all the centralized solutions.
Sorry but if you want private messaging Signal is your only option. I'm sorry you all have to deal with it but now is a good time to bully friends and family into switching to Signal.