My son thinks he is a "Skibidi Toilet"

I've taken him to several therapists but nothing works. My son thinks he is a "Skibidi Toilet". He honestly and truly convinced he is one of these singing toilet creatures, and will not stop insisting that everybody else believe him too. It is relentless and unnerving.

My kid used to be smart and bright but his mental capacity is waning because of this. I fear for his future development and potential growing into an adult. I used to expect a "hello" or "good morning" from him, but now all I get is a ""Skibidi dob dob yes yes yes, Skibidi dob dob dip dip" ... you know, "Skibidi" this and "Skibidi" that. I've had it with this stupid ♥♥♥♥♥♥♥ song and everything.