That’s notification spam.
Web sites cannot perform malware scans, as that is inherently deeply intrusive, and thus is blocked.
Any websites or any pop-up ads that are claiming to perform remote scans are lying.
So what happened here? Somewhere along the path, you were offered and accepted notifications from some website or its ad networks, and the advertiser is using those notifications for spam, and now you no longer wish to receive those notifications.
Here is how to shut off notifications, and also how to block future requests to send these notifications:
Stop unwanted Notifications - Apple Community
There’s no malware here, so nothing needs to be done after the notification is removed.