We use Hetzner internally for development. At the time of planning and migration Hetzner's Object Storage offering was not GA which was technically a deal breaker. Maybe we can consider Hetzner for our EU multi-cloud

You could have used Cloudflare R2 for object storage and Hetzner for almost everything else.

Sure but as soon as you cross the boundaries of your provider both cost and latency start to ramp up ;)

Though I dont think there are such boundaries at R2? They openly state what they charge for. And what they charge for is not egress. Its storage and operations, and they have very generous pricing.