Looking for logging into the Multisite 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 Multisite site. After that you can login as usual with your login credentials.
https://wisdmlabs.com/blog/common-login-logout-in-domain-mapped-multisite/
https://codex.wordpress.org/Multisite_Network_Administration
https://wordpress.org/support/topic/multisite-have-to-re-log-in-to-sites-on-network/
https://wordpress.stackexchange.com/questions/259839/cookies-in-multisite-where-network-sites-have-their-own-domain-name
https://objectiv.co/fix-cant-login-converting-wordpress-multisite/
https://halfelf.org/2012/multisite-login-loop/
https://mathias-kettner.de/checkmk_multisite_login_dialog.html
https://www.drupal.org/project/multisite_login
https://tommcfarlin.com/resolving-the-wordpress-multisite-redirect-loop/
https://premium.wpmudev.org/blog/ultimate-guide-multisite/
https://kinsta.com/blog/share-logins-wordpress/
https://wpengine.com/resources/wordpress-multisite-user-management/
https://www.quora.com/How-can-I-build-a-single-page-multi-site-login