$ gh release view -R open-policy-agent/opa --json assets v0.64.0 -q '.assets[].name'
opa_darwin_arm64
opa_darwin_arm64.sha256
opa_darwin_arm64_static
opa_darwin_arm64_static.sha256
opa_linux_amd64
opa_linux_amd64.sha256
opa_linux_amd64_static
opa_linux_amd64_static.sha256
opa_linux_arm64_static
opa_linux_arm64_static.sha256
opa_windows_amd64.exe
opa_windows_amd64.exe.sha256
https://github.com/open-policy-agent/opa/releases/tag/v0.64.0
The asset
opa_darwin_amd64wasn't released.