So what if we don't know? We can find out at the same time.
We're trying to authenticate a pair: user/pass.
There is no pair for the enterprise users signing in with their company's SSO or those using Passkey.
I think what some sites do is have a visually hidden, not required password field that a password manager can fill in. If it's not a password-based auth, the flow goes to the next step but if it is, it reveals the password field which may already be filled in.