https://github.com/apple/pkl-go/blob/v0.6.0/.circleci/config... seems to imply it's "curl && chmod" so maybe you're thinking of developing pkl itself?

I happened to have a container that I am certain contains no Java and it fired right up

  $ docker run -it --rm --entrypoint=/usr/bin/env public.ecr.aws/aws-cli/aws-cli:2.15.38 bash -c 'curl -fsSLO https://github.com/apple/pkl/releases/download/0.25.3/pkl-linux-aarch64; chmod a+x pkl-linux-aarch64; ./pkl-linux-aarch64 --help'
  Usage: pkl [OPTIONS] COMMAND [ARGS]...