Enabling an auth method shouldn't prevent you from using others, but if you enable fingerprint auth via #fprintd, privilege escalation commands like #sudo don't let you use a password anymore to authorize actions; you must use a fingerprint (until the fingerprint request times out)
#PolicyKit dialogs show a useless "Authenticate" button that never actually gets clicked, but not a password entry textbox (until after fingerprint auth fails)
The UI is already there, just show it!