Youtube is a monopoly because it's not a very good business to be in and it basically lives off Google subsidization. It has plenty of openings for competition and none have too much forward movement.
Revenue. From earnings release for 2024 Q3[1]: "YouTube's total ads and subscription revenues surpassed $50 billion over the past four quarters". 2024 Q4 says: "Together, Cloud and YouTube exited 2024 at an annual revenue run rate of $110 billion."