vax cards have been standard operating procedure for international travelers for eons

for vaccine records, driver's license, insurance cards, and other simple forms, like professional licenses, to be digitally available. Because the data originates at the appropriate state agencies, it carries the imprimatur of a "passport," which would be very difficult to "counterfeit," and should be accepted just about anywhere.

Of course, you have to verify that your pharmacy, clinic, provider actually reported the pertinent information. One of my doses, while reported, did not include the lot number. I was able to send a photo of the receipt to the state health department group overseeing it and they added the information.