Just like US companies can run computers outside of the US border, so can other companies. A German CDN can setup their own infrastructure within US borders, then German companies can work with that CDN to speed up connections within the US for users coming from there.
> There is no way to avoid this.
There is. GeoDNS ("Regional Records") is one way, where you reply with different IPs to the instances based on where the DNS query comes from. So US visitors to domain.com gets a different IP than German visitors to domain.com.
> What can German indiemakers do now? Register a company outside of the EU?
Use European infrastructure, make sure you follow GDPR. As a fellow European (mostly) "indiemaker", it's really not that hard.