RPGMemes

I'm on team "tell the players", personally, because it lets the players customise their characters for the module. A group for Wilds Beyond the Witchlight are going to be different from Descent Into Avernus, for example.

(Of course, if a player decides to put Doom Guy in a fairy tale, that's perfectly fine, but it should be their choice.)

Also, a person who knows about Tomb of Horrors will figure it out pretty quickly during gameplay anyway because of those set pieces you mentioned, so it doesn't matter if you didn't tell them what it was. Heck, they might even have bowed out so they don't ruin things with their meta-knowledge, if only they knew what they were going to be playing.