Choose New item > SSH key to store a private key, its public key and its passphrase. Each is encrypted in your browser like every other Password Vault value.
Paste a private key in OpenSSH format, the format ssh-keygen writes, and the public key is filled in from it. The item shows the key type, such as Ed25519 or RSA, and the same SHA256 fingerprint that ssh-keygen -l prints. It says when a key is protected by a passphrase, and when the public key does not match the private key.
Generate key on a new SSH key makes an Ed25519 key in your browser, without a passphrase. Copy public key on the Password Vault list copies the line to add to a server or Git host.
The Magpie app can store and show SSH keys too. Keys are generated on the website only.