I will give you a scannable QR code for the EU covid app (works with most of them), but will most likely show a red chechmark, but also a scannable QR code for Apple Wallet, which shows the pass as valid, and is usable everywhere (literally everywhere)
>name >dob >vaccine manuf >doses/max doses >eu state >certificate issuer (usually ministery of health of x but can be whatever you want)
pic related is scannable by EU apps, will post the apple wallet qr code below. let's make some memes