Sometimes a little icon appears in the notification area which when clicked opens the browser to a page about plasma integration.

I am not interested and would like to get rid of that icon permanently. How to do that?

Which Browser is this, Firefox? And which Plasma version? Which distribution? All essential informations when asking a question...

If you are using a Neon installation, it is recommended, else there should ba a package called plasma-browser-integration, just removing this should be enough AFAIK

FWIW: careful with your wording, calling a perfectly legit notification "spam "is a bit much...