Hi… I may be misunderstanding what you’re trying for, but --local-only doesn’t actually run the application on your local machine.
Instead, it compiles locally, but then still deploys to Fly.io’s x86 Linux servers, 
.
In the past, there have been a lot of problems with local x86 compilation on ARM hardware.
(Indeed, that’s why remote builds are now the default.)
Hope this helps a little!