Try PRIMARY_REGION=lax (typically used for Fly-automated Postgres) in your fly.toml and see if fly deploy --strategy immediate then does the right thing in deploying to lax (ref).
fly deploy isn’t quite the command I’d use to set regions. You probably know this, but the specialist command is fly regions set ...: VMs not redeploying to specified region - #4 by Yaeger
If you’d like to add a region, then you’d use fly regions add ...
For setting up backup regions and list existin regions, ref: Avoid a region - #2 by kurt
And to set one vm per region, see: Scaling not prioritizing primary region - #8 by kurt