VPS
SSH keys on a VPS
Public keys at order time. Private keys never leave your machine.
At order
Paste an OpenSSH public key (the .pub file, one line starting with ssh-ed25519 or ssh-rsa) when you deploy, or pick a key already saved on the account. Steady never asks for a private key and will reject one if sent by mistake.
If you skip a key
A one-time password may be stored when the platform issues one. Collect it from the server page, log in once, set a key, then disable password login. Do not leave the one-time password as the permanent access method.
Several people
Each person should have their own public key in authorized_keys. Do not share one root password in a chat. Remove keys when someone leaves the project.