The Github webpage shows on every repo's insights page what repos are dependent on it: https://github.com/django/django/network/dependents
Via the Github API you seem to only get the repos that your repo depends on not the repos that are dependent on your repo. See Repository.dependencyGraphManifests:
https://docs.github.com/en/graphql/reference/objects#repository
Did I miss something or is it just not possible to get the dependents via the API?