My guess is you somehow turned off Joomlas core user plugin or configuration.php is incorrect. Using phpmyadmin navigate to the _extensions database table and find the extension named "plg_user_joomla" and set its "enabled" column to 1. In that same table find extensions named "plg_twofactorauth_totp" and "plg_twofactorauth_yubikey" and set their "enabled" columns to 0. That should ensure Joomlas core user plugin is enabled and 2FA is turned off. Next edit configuration.php and ensure $live_site and $cookie_domain are both set to '' (basically an empty string) then set $captcha in that same file to '0'. If still not working I suggest posting to the Joomla forums below.
forum.joomla.org/
krileon
