from Thread solution Blacksmoke16 on Crystal Lang Forum:

Is it an option to try installing Crystal via brew? Or the universal tarball: https://github.com/crystal-lang/crystal/releases/download/1.16.3/crystal-1.16.3-1-darwin-universal.tar.gz?

Otherwise may just need to wait for someone more familiar with asdf.

this worked for me, installing via brew install crystal and running:

$ crystal build src/early-registration-api-cr.cr

# outputted `./early-registration-api-cr`

$ ./early-registration-api-cr
2025-06-17T20:57:32.860804Z   INFO - kemal: [development] Kemal is ready to lead at http://0.0.0.0:3000