Hi… This sounds like it’s probably the builder, which is created closest to where you personally are—regardless of the app’s primary region, etc.
There’s an environment variable that can be set to override that separate default:
https://community.fly.io/t/region-cannot-host-your-machine-fra/23071/31
(Maybe also try --build-depot=false.)
Alternatively, you can build first, push the image, and then pass the resulting registry.fly.io/<long-string> ID to fly machine run in place of the . positional argument.