When trying to sync or copy images with --sign-by-sigstore-private-key using a key that doesn't have a passphrase I get the error

FATA[0002] Error copying ref "docker://ghcr.io/siderolabs/glibc:2.41": private key passphrase not provided

The same key works with cosign via

cosign sign -y --key cosign.key $IMAGE

If my key has a passphrase the error is not shown and copy continues.