Users without JavaScript, cannot currently see cross-wiki notifications in [[special:notifications]], and cannot access the flyout/popup.
They currently have to go to each wiki they've edited/visited, to find out where the notifications are coming from.
This should be fixed, as part of T115316: Better organisation of the Notification Page
(Example of the issue encountered, in https://en.wikipedia.org/w/index.php?title=Wikipedia:Village_pump_%28technical%29&diff=721278609&oldid=721277306 )