Windows

If you are getting lots of pop-up messages on the right side of your screen when you start your browser, you may have allowed 1 or more web sites to show you notifications. Often these are alarming messages about viruses or expired antivirus, but they are fake malware messages.

You can disable all browser notifications in Settings:

Locate the browser you are using (Microsoft Edge, Google Chrome, Mozilla Firefox) and toggle the button to off

Reference: https://support.microsoft.com/en-us/windows/change-notification-settings-in-windows-8942c744-6198-fe56-4639-34320cf9444e