I cloned a live site here https://www.nemgtr.org into a new site - got the database and config file customized, but when I go to the first url listed below I get an error message...if I add index.php on the end it works. I searched and searched, but none of the fixes worked

https://staging2.nemgtr.org/ (not good)
https://staging2.nemgtr.org/index.php (good)
I noticed when clicking the link on the admin page at the very top right of the page (to open the site in a new window, it does not have the "https://" in the link and it opens the page (without the index.php) and shows that it's "Not Secure"

I wonder if these tow things are working together to make a less than favorable outcome...how do I change that link at the top right of the admin page?