Hi… The usual advice is to try fly deploy --depot=false, which will give you one of the freebie legacy builders.
If it still complains about capacity, then try the FLY_REMOTE_BUILDER_REGION environment variable:
https://community.fly.io/t/region-cannot-host-your-machine-fra/23071/31
(Maybe add in --recreate-builder, just for completeness…)
Hope this helps!