NopCommerce generates a robots.txt file that tells Google what it can/cannot crawl, you can view your site's file by going to:
http://yoursite.com/robots.txt
If you haven't made any modifications it does not explicitly disallow "login?", but you can add a custom "robots.additions.txt" file that NopCommerce will append to the one it generates.
E.G. create a txt file in notepad named "robots.additions.txt" with:
Disallow: /login?returnUrl=*
And save it in your site's root directory (where Nop.Web.exe lives).
If you want to bypass the built-in robots.txt and roll your own, name it "robots.custom.txt" and NopCommerce will use it instead, but I don't recommend doing that. There are a lot of default links you don't want any bot crawling.
You may also want to sign up for Google's search console so you can see what it sees:
https://search.google.com/search-console/welcomeGoogle should be assigned to a built-in search-engine account, but if it's being considered a Guest account and you have Guest navigation disallowed in ACL settings then it's going to be redirected to login for every single link it finds.