Oh just because sandboxed google services is installed doesnt mean your payment info is shared between different applications/websites assuming proper encryption on their end. If you want to improve your privacy for electronic payments like others said monero is best but since thats not widely used yet a card masking service is what you want for now. However you'll be relying on a third party, privacy.com is what the majority use afaik. As for gpay, privacy from google is basically nonexistent, obviously, but if you mean privacy from merchants then they already mask your card information for transactions iirc. I suggest either using a card masking service, another electronic money service such as paypal (shit privacy but you wont be tied to google), or even using a prepaid visa gift card or giftcards in general paid in cash at your local drugstore.