Main advanced search cannot and should not cover all potential situations that are specific to applications available in Maniphest, and I can imagine that the logic to update the displayed options on-the-fly based on the "Document Type" chosen would be rather complex, and instead showing all application-specific items and having them greyed out based on the "Document type" chosen would make the displayed search area huge, something that was already criticized in T76137.
I'm declining this as the design makes sense - for application-specific searches and getting those options that only make sense for that specific application, it is recommended to use the application-specific search.

@Nemo_bis, you keep reopening this task because

https://phabricator.wikimedia.org/search/query/advanced/ should be consistent. Either all fields allow "none", or none does.

As we have seen in this discussion, Andre and me don't agree with this. We don't think this is a requirement, and we don't think we should file this request upstream in the name of Wikimedia. We are not going to hack Phabricator and maintain a local patch for this either. If you want to create a request upstream, you can do it at your own risk, and have this discussion with the maintainers directly.

I don't think there is anything left to be discussed here. If you want to watch orphans, save this query: https://phabricator.wikimedia.org/maniphest/query/RFEPiqxQuXUi/#R