Try this:
One solution is to change your theme functions file (/wp-content/your-theme-name/functions.php), replacing the reference to wp-pass.php with wp-login.php?action=postpass. This has worked successfully on one of the sites that I manage.
Your password protection may be in another functions.php file in a different folder. I found my password protection in
wp-content/themes/themename/lib/functions/functions.php
https://dmjcomputerservices.com/blog/do-you-password-protect-your-wordpress-posts-or-pages/
