a room is a situation to me, and 'What here is not what it appears to be?' does fit searching for secret doors
I generally agree with this, and would point to "Discern Realities" as a move to invoke in the face of an action declaration of, "I search the room for a secret door." In my mind the assumed situation is, whether declared by the player or not, "To better understand the situation of how monsters / people are tracking in and out of this space."
However --- in the context of a DW resolution, in many cases I wouldn't tie the success/failure of the roll to the discovery of the door itself.
They're in the room, there IS a secret door, they're expressly asking to find it. Unless I as GM have pre-authored that the door is not findable through any normal means (prodding, probing, tapping, listening, magic), like, simply making the action declaration means they should find the door.
The change in thought process is how, as a PLAYER, I expect to see the
hard fail 6- result shown on the dice. I should NEVER assume as a player that dice roll won't have real consequences---and if it's a 6- fail, it will be
hard consequences from the GM. As a player of DW, I should expect resolution of a "move" to keep any and all situations dynamic/fluid.
Contextually, in the fiction, I've basically established that my character should have every reasonable expectation to find the door, but I roll a hard fail 6- on the dice.
In D&D terms, GMs are trained to say, "Nope, there's no door there." Regardless of any downstream consequences to continuance of the party's success.
In DW, GM says, "Sure, you find a door . . . ."
Now insert hard GM move to reflect the roll of the dice.
Conversely, if they roll a 10+, suddenly not only have they found the door, they've also discovered something unique, interesting, and useful to future actions. They've found an interesting set of tracks/marks indicating what's ahead, there's something clear about what the tunnel is used for in connection with their current stakes/scene frame, there's a connecting clue hidden in the space behind the door that's useful, etc. etc.
Now again, is this all possible without the specific framework of a DW "move"? Well, yeah, of course. But in a game of 5e, it's all on the GM to actively choose to do this of his/her own free will. In DW, aspects of these kinds of responses are hard coded into the resolution of the move.
Every throw of the dice in DW is a risk. You are potentially forcing the GM's hand to
reveal future badness, or
carry through on a threat, or any of the identified GM moves.
*Edit --- now, it is also at the GM's discretion for 6- result on "Discern Realities" to indicate full failure to find the door AND include heavy GM badness. That's available to the GM as well, depending on circumstance. I'm just saying that in a lot of cases, DW may have a different mindset entirely than a "traditional" mindset.