https://phabricator.wikimedia.org/maniphest/query/wqKvWfbDNl.E/#R is a good approximation, optionally with the "Updated Before" field.
Specifically, tasks that have seen little activity at all, with said activity shortly after their creation. Tasks such as https://phabricator.wikimedia.org/T170846, or https://phabricator.wikimedia.org/T147490, which are old and out of date and can be closed.
I'd like to browse a list of those and see how many I can close. (Mostly because I want to see the number "Open and stalled tasks in total" in the Phabricator monthly statistics decrease)
@Mainframe98 Heh, I appreciate the intention! :) https://phabricator.wikimedia.org/T248034 comes to my mind...
It depends a lot on how you define "dormant". The most simple way (and definition) would be querying for open/stalled tasks and order by "Date Updated (Oldest First)": https://phabricator.wikimedia.org/maniphest/query/wqKvWfbDNl.E/#R
That task is useful, thanks. I see the search form has a "Updated Before" field, that allows relative values too. Perhaps I can do something like "Updated Before: 4 years".