Hi the password admin backend doesnt work its not protected and you can login as normal /administrator without get redirected protected there.
see attachment and testing with latest Joomla 3.9.27 and php 8.0.3 and Admin tools 6.0.6
[02-Jun-2021 09:10:34 UTC] PHP Warning: FOF40\Download\Adapter\Curl::reponseHeaderCallback(): Argument #1 ($ch) must be passed by reference, value given in /home/sflnojcm/public_html/libraries/fof40/Download/Adapter/Curl.php on line 135
[02-Jun-2021 09:10:34 UTC] PHP Warning: FOF40\Download\Adapter\Curl::reponseHeaderCallback(): Argument #2 ($data) must be passed by reference, value given in /home/sflnojcm/public_html/libraries/fof40/Download/Adapter/Curl.php on line 135