I have seen some that seem to be doing that kind of thing, but many others that will reject a bad username before asking for a password.
To double check, I just now tried putting a known bad email address into the username field for amazon.ca and was not then asked for a password, but told that no account could be found.
My possibly flawed understanding of login security is that a failed login should reveal nothing about why the login failed in order to prevent information leakage that can be exploited.
Amazon allows 2FA, but I’m pretty sure they don’t require it.