The suggestion by Tech wouldn’t work for the particular issue that you are experiencing with the Avast Online Security (AOS), but it should prevent other popups piggybacked to the auto update function. However without a screenshot of these other popups, it is hard to say what is initiating them.
It would probably be best to uninstall the AOS plugin/add-on. This is called the Browser protection in the avast custom install/uninstall.
To uninstall an element in avast - Windows Control Panel > Programs & Features > avast antivirus - Uninstall - Change, from this new window, uncheck the Browser Protection feature.