Since T120013, https://phabricator.wikimedia.org/maniphest/task/create/ is a 404.
It should rather redirect (keeping URL parameters intact) to https://phabricator.wikimedia.org/maniphest/task/edit/form/1/ I think.

We've advertised them a lot across wikis etc I'm afraid, especially with parameters like https://phabricator.wikimedia.org/maniphest/task/create/?projects=Developer-Relations which now require https://phabricator.wikimedia.org/maniphest/task/edit/form/1/?projects=Developer-Relations so if we do not redirect, we need to fix quite some docs across wikis.