This is a typical IT support scam case. Your computer was not "locked" up. It is just a pop up page that can have some audio effect (sometimes) and display in full screen mode, so it appears the computer is locked. When that happened, you can just hold down Ctrl+Alt+Del, then launch Task Manager, and then end all browser items there to close it. But as long as you didn't call the number or engage in any of the requested activities, your computer is not ok.
Scammers use various methods to trigger these pop-ups. Pop-ups are a form of online advertising. They are often integrated into websites or applications through ad services. Many websites use third-party advertising services to display ads. Sometimes, these ad services might inadvertently allow scam ads to be displayed. This does not mean the website itself is malicious, but it indicates a lack of stringent ad vetting.
You can read more about this type of support scam here: https://support.microsoft.com/en-us/windows/protect-yourself-from-tech-support-scams-2ebf91bd-f94c-2a8a-e541-f5c800d18435