I have a question, did you install any software from a website that you can't trust/don't know? If you did did it say something like"You need to update to the latest version of Flash Player!"
if you were trying to download a file on the internet and you were redirected to another tab saying "click here to download" or "click allow to download" if you clicked "click here to download" then open the browser you downloaded the file from and go t the extension settings and then if you see any extension that you didn't download or a extension you don't trust or are suspicious of, delete that extension. If you clicked on "click allow to download" then open your browser that you downloaded the file from > > notification access. if you see any fishy or unknown site, block the notification on that site. And that's it! I hope it helped! And if you still have popups, download a free or paid anti-virus An example of a free anti-virus is Malwarebytes. The reason the popups are happening might be a browser hijacker extension that you might have installed. to see if your browser is hijacked, type anything random in the text box and if you see "Google Search" in the right side of the text box, your browser is not hijacked. if you see something else like yahoo search or bing or something else, your browser is hijacked. when your browser is hijacked all the search results will be fake or scam websites instead of genuine official websites. an example is if you search for an airplane ticket on a hijacked browser it will show scam results meaning the websites will be scam websites. they will take your money and not give you the ticket. Stay safe! And I hope this helped!