"To be announced" means that this game is in the Alpha/demo stage and not in the "Early Access"/mostly playable stage! Those downloading it should consider it as a "preview" of a game that may be worth looking into! For more information, see here.
Update 02/03/24: The term "Coming Soon", equivalent to the term "To be announced", has been revamped by Steam. See my conversation with Kain Yusanagi concerning the term "Coming Soon". Please read the entire conversation (I only linked to my closing comment earlier but please feel free to read the entire conversation in the game page for the purpose of clarification, starting with the first comment) and then decide for your own purposes what the term really means to you. As for myself, I'll still think of it as an announcement of a game preview.
I have nothing against those two tags, Just saying the story does not involve a male dick.