(I've updated Tasker to version 5.12.8-beta, with no change to this issue.)
I've made a task in Tasker called "Radiator" which, so far, just executes a Say action.
I've made a routine in Google Assistant that's started by me saying, "Hey Google, I've turned the radiator on", and which responds with the "Try adding your own" action "Run Radiator in Tasker". (I've also tried using "Do" and "Start" instead of "Run", with the same lack of results.)
Google assistant responds with search results for "Radiator".
This is also happening with other Google Assistant routines invoking Tasker that previously worked as expected.
(Further, delving into the Explore settings for Google Assistant and searching for "Tasker" brings up a "Run test in Tasker" example which, when clicked, also gives me a search result – and I do have a task called "test" in Tasker.)