Hi, thank you Kuldeep? .
I finally resolved the issue. Following the instructions provided above, I verified that the folders were set to 755 and recursively inclusive. After restarting the plugins and themes, I decided to reset the web config as well. Surprisingly, this allowed for successful login, and the backend functions properly.
So, my solution involved pasting the web config file again and using the default file from this URL: https://gist.github.com/Toddses/7f3729ddf7c6466bb3dc. Additionally, I utilized the IIS interface system to have IT personnel adjust relevant permission settings. As a result, the backend login works correctly now. Great news!