Even in the US, a corporate monopoly trying to force people to use their browser will trigger an antitrust lawsuit from the government. Microsoft has already faced one for what they did with Edge, and they didn’t even do DRM.
Besides, it’s YouTube. If you can’t use it anymore, it’s not gonna be the end of the world.
Three percent of all browsers is a fuckton of users, considering that includes mobile users who are going to be less likely to change their browser then desktop users. There is an estimated 6.92 billion smartphone users. Three percent of that is more users than there are people in the United States.