What is the Russian equivalent of the English idiom elephant in the room which means (according to Wikipedia)
important or enormous topic, question, or controversial issue that is obvious or that everyone knows about but no one mentions or wants to discuss because it makes at least some of them uncomfortable and is personally, socially, or politically embarrassing, controversial, inflammatory, or dangerous.
Just recently I heard on some news station something like this:
The obvious elephant in the room is president Biden's mental condition.
The only thing that comes to my mind are the emperors's new clothes (новое платье короля) from the fairytale by Hans Christian Andersen.