I think, with all respect, that you have to educate yourself on this subject. An app is usually just a client, for some other service that runs somewhere on the internet.
Ok, not a calculator-app, because that one can run without any outside support.
But most apps, they use some kind of host. If that host can be anywhere in the world, then it is fine. However, if it is bound to a specific host, like WhatsApp, Signal, Telegram, you are locked in by some vendor, with a host that is placed in a country that might not so pleasant to do business with.
An email-app however, is usually not restricted to one host. You can tell it which email-provider you want to use, and that can be anywhere in the world. Don’t like gmail? Then use another provider, or ultimately, host an email server yourself.
The same applies to the messenger app Matrix. It is not restricted to one host. There are hundreds of hosts. I self-host a Matrix instance in Iceland, and just like with e-mail, it will communicate fine with any other instance where my message partner has chosen to subscribe to.
Anyway, I urge you, do not advocate “European services” because that is just moving the problem from one place to another. To really solve the problem, we have just to go back to how the internet was intended, and only promote decentralized services that can be anywhere on the world (you pick one you like), with an open standard, so there can be multiple clients using the very same service.
I self host my email server. I use Thunderbird on my laptop to access it, and K-9 mail on my GrapheneOS phone. I’m not bound to just one provider, nor to just one client app.