“Google may begin withholding U.S. taxes on earnings you generate from viewers in the U.S. as early as June 2021. Please submit your U.S. tax info in AdSense as soon as possible. If your tax info isn’t provided by May 31, 2021, Google may be required to deduct up to 24% of your total earnings worldwide. If you’re a creator in the U.S., you may have already submitted your tax info. Check your tax info in your AdSense account to be sure.”
If your country doesnt fall under a tax treaty then the rate may up to 30% but wont count worldwide. You could calculate for yourself if its worth to acceot the higher (submit) rate or not (dont submit fomular).