[tracker1]

I've found that having the "username" visible along with a hidden "password" field, then keeping that after confirming the user is a password based user on the password entry screen is generally helpful for use with a password manager.

    [Username] Visible
    [Password] Hidden
    [Next] Button Clicked
    |
    V
    Server checks username and user type (password case)
    |
    V
    [Username] Read Only
    [Password] Visible, with any previously submitted value
    [Login]
    

Similarly for account registration, with a hidden username field and a visible password field if separating the password and account initial entry.

Just my own experience with a lot of experiments on implementing an authentication system and supporting a password manager for self-serving purposes.