Oh boy oh boy. Did you know that password protected SSH keys regularly store the password hash as md5sum? (Except for ED25519 keys). Well, I didn't.
If your private key starts with something like
Proc-Type: 4,ENCRYPTED
DEK-Info: AES-128-CBC,CB973D5520E952B8D5A6B86716C6223F
yeah, that's the kind. You can re-key though by running
ssh-keygen -o -p -f .ssh/my_private_key
Source and good further information here: https://latacora.singles/2018/08/03/the-default-openssh.html