Shady converter sites abuse Chrome's notification permission to push spam to your desktop. Removing the permission takes under a minute. Here is exactly how.
Click the three-dot menu in the top right of Chrome, then Settings.
Go to Privacy and security, then Site settings.
Scroll to the Permissions section and click Notifications.
Under "Allowed to send notifications", find the spammy site. Click the three dots next to it and choose Block or Remove. The spam stops immediately.
Tap the three-dot menu, Settings, Site settings, Notifications. Find the site and turn its permission off.
Other browsers: see the cleanup hub. Learn how the trick works: fake download buttons.