How do I convert an OpenSSH-generated ED25519 key to the PEM format?

I am trying to convert an OpenSSH-generated private host key to the PEM format, so that I can use it also in dropbear-initramfs. However, when trying to do so using the ssh-keygen program, I am getting an error as follows: …# ssh-keygen -m PEM -e -f /etc/ssh/ssh_host_ed25519_key >/root/ssh_host_ed25519_key do_convert_to_pem: unsupported key type ED25519 How can I perform this operation?