If "Investment bank Evercore ISI estimates Apple will have a $30 billion ad business by 2026" is correct, then $30 billion/$391 Billion is over 7%.
If we go by the 2022 publication number (so likely from 2021) of $4 billion then yes, that's about 1%.
I can't find concrete numbers. https://www.emarketer.com/chart/260183/apple-ad-revenues-wor... has 10 billion in ad revenue for 2024, which would put it at 3% last year.
https://www.investors.com/news/technology/apple-stock-advert... says "he sees Apple's global ad revenue hitting $19 billion by 2026" which would be 5%.