Some sites trick users into accepting notifications.
But users don't realise that this can mean advertisements for things not associated with the original site and often trying to sell or scare users into thinking they have security issues.
The usual way to stop this is to:
Left click the 3 stacked dots just below the X in the top right hand corner
Near the bottom of the box that opens left click "Settings"
Scroll down to the bottom of the Settings page that has opened and left click the word "Advanced"
In the "Privacy and Security" box left click the words "Site settings" (or "Content settings")
Then go down about 6 settings and left click the word "Notifications"
Left click on the little slider on the right to make the word "Blocked" appear on the left.
Close Chrome with the usual X in the right hand corner.
A quick way to get there is to type the following in the top entry box of Chrome: