withholding tax means you (the developer) lose 30% + itch.io % + paypal or Stripe fee. No one in the USA gets withhold tax fees, however most common indie developer uses one of these listed in the IRS website https://www.irs.gov/businesses/small-businesses-self-employed/sole-proprietorshi...
The person who buys your game/art will not do anything, only you are taxed.
If your country has an agreement with the USA to lower your tax, you should take it as it can save you money.