General problem: In all FOSS projects I've worked on I've seen cookie licking in task trackers: Folks set themselves as assignees but never ever manage to work on the task. Other folks are interested in working on the task but they think that the assignee actually works on them. And in the end nothing ever happens.

Phabricator is already helpful by displaying the "Assigned" query on the Maniphest front page by default. There are also well-organized projects out there that manage to apply ideal best practices in software management.
Still I unfortunately don't see all devs in all projects go regularly through their list of assigned tasks and clean up their plates themselves. Especially not in projects that rely on volunteers who sometimes show up again after months, sometimes never again (AWOL / MIA) and in established and large projects that have a long backlog.

So as a triager I'm used to jump in and (mass-)add some "Are you really still working on this?" comments on stuck tasks or directly remove the assignees from stuck tasks.

Request: Other task management tools allow me to query for open tasks with the "assigned to" field not empty && specifically the "assigned to" field not changed for a certain time (like 6 months). Note that searching for "Updated before" won't help as other folks might have added comments like "Assignee: Are you still working on this?" without receiving an answer.

Any way to find such tickets would be welcome (maybe it exists and I'm too stupid to find it?). I don't want to clutter the Advanced Search UI, so if at least Conduit supported such a query I could probably hack up some custom script.

I'm aware this is a specialized request but IMHO it's vital for project management and general healthiness of a long-running (FOSS) project to be able to identify such tasks (and assignees) and get them out of the limbo, or at least clarify/lower expectations towards the task subscribers and author.