One of the EU's primary revenue streams is periodically (annually?) being "tough" on Big Tech. If you can't build - regulate, or something like that.
So that's ~4%. It’s not insignificant, but I wouldn't exactly call it a primary revenue stream. VAT brings in 3x as much money. Import duties bring in about 5x that. And about half of the budget comes directly from the member states.
"Tech fines tracker" - https://proton.me/tech-fines-tracker