Looking for logging into the Github Pages 404 site and are not getting the correct working link for it? In such a case, you can use the links given here by searching your desired login page in the search box. If the page is present on our website then you will get all the links related to the Github Pages 404 site. After that you can login as usual with your login credentials.
https://stackoverflow.com/questions/11577147/how-to-fix-page-404-on-github-page/45907768
https://help.github.com/en/articles/creating-a-custom-404-page-for-your-github-pages-site
https://github.community/t5/GitHub-Pages/Getting-a-404-error-on-my-page/td-p/9860
https://github.community/t5/GitHub-Pages/index-html-not-working/td-p/1266
https://github.community/t5/GitHub-Pages/I-am-getting-a-404-error-for-my-Github-Pages/td-p/7198
https://github.community/t5/GitHub-Pages/gitHub-pages-URL-404/td-p/4466
https://www.reddit.com/r/github/comments/7rrkl7/github_pages_404_error_with_right_username_and/
https://webapps.stackexchange.com/questions/109012/404-error-when-trying-to-access-my-github-page
https://jekyllrb.com/tutorials/custom-404-page/
https://discourse.gohugo.io/t/hugo-site-on-github-pages-404-error/13200
https://discuss.codecademy.com/t/404-error-github-page-not-showing-help-please/326662
https://mycyberuniverse.com/developing/custom-404-page-for-website-hosted-on-github.html
https://www.freecodecamp.org/forum/t/github-page-error-404/253356