I expect applies to any app on a phone that is registered in the EU. If you wanted to and were able to buy a Swiss phone with Swiss number you might be okay.
Developers could start to employ software activism and dis-allow licenses for software they develop by European governments citing the reasons.
Perhaps Signal can deploy a version for Europe that is licensed for use only by governments and scans the hell out of them looking for corruption using AI.
Well, I goofed. Nonetheless, Threema is claiming GDPR-complaince:
Excerpt from their main web page:
Threema is 100% Swiss Made, hosts its own servers in Switzerland*, and, unlike US services (which are subject to the CLOUD Act, for example), it is fully GDPR-compliant.
Make no mistake I would never use Threema, and "made in switzerland" is usually just putting lipstick on a pig; the one time someone seriously looked into Threema it was full of weird decisions, if I remember correctly
Still GDPR is unrelated to what we are talking about
Yes, everyone wanting to serve clients in the eu (even if they are on vacation in non eu) must comply with the gdpr; this article however is not related to the gdpr though.
It just means you only store the data you need, you track how the data is used, and you allow data subjects the possibility to modify/remove said data.
EDIT: Switzerland is not a member of E.U.