Easy unmemorable throwaways. Plenty of services will tell you that your chosen screen name is taken and automatically offer the same thing followed by numbers, “UserName123” for instance.
Ooh! Yeah that's hella sus. It's also the Fox News youtube channel so surely they have an army of bots to drive whatever narrative they're spinning that day.
That’s just the default. At some point a while ago I got a pop up about making a username, which for YouTube I don’t care about at all. So I just clicked the button accepting whatever it gave me.