I think im getting the same or a similar error.
Once i hit submit after inserting admin/pass
the
/wp-login.php
url displays
“Found
The document has moved here.
Additionally, a 500 Internal Server Error error was encountered while trying to use an ErrorDocument to handle the request. “
(The “here” is a link, wich dont log you in at all.)
The problem is somehow solved by hitting the back button… but users who never been to site before dont know this. And this error replicates it self to other areas of site. Like when i activate plugins.
if i go back to my url/install folder
https://www.misjonskirken-narvik.net/wordpress
i see the page and im logged in
as admin and can access back-end