On macOS (put your FIDO2 PIN when asked):
ssh-keygen -t ed25519-sk -C "mailbox@address" -f ~/.ssh/id_ed25519-sk
Probably you'll see this error:
Generating public/private ed25519-sk key pair.
You may need to touch your authenticator to authorize key generation.
No FIDO SecurityKeyProvider specified
Key enrollment failed: invalid format
You have to install SSH via Homebrew:
brew install openssh
