GitHub allows any users to post Issues but allows tagging and notification options only for users who have been added as collaborators on the oceanmapping/community repository.
Simply contact the admins (https://github.com/oceanmapping/community/wiki/Contributing) to be added as a collaborator. Then sit back, relax, and enjoy Issue tagging and notifications among many of the wiki's all-inclusive benefits.
(Thanks to Mike Smith and Lindsay Gee for pointing out this nuance of the Issues section.)