It's pretty clear that using AWS is lawful. What you're questioning is if AWS is being used in a compliant manner, which is an entirely different thing. It is possible to do so, so there's nothing odd with choosing AWS.
Personally I find it odd to choose AWS (and Cloudflare) for running a privacy-focused service out of Germany. But again, that's just my personal opinion, I guess most people here are fine with this setup. And I'm also at least a bit doubtful that a one-person startup can get all compliance aspects of running services in a global AWS and Cloudflare-based setup right, so I'd recommend using infrastructure that by default will be hosted in the EU so you don't have to worry about this.
