One gotcha with some of the app stuff is that, especially for scan and pay, the barcode is dynamic and you can’t avoid the app. I know that’s the case for the 7-eleven app and its barcode for loyalty/scan and pay.
Edit: also, it’s free.
I've had patchy success with adding boarding passes to the wallet too. Support seems half baked.
EDIT - I think this is the case. When I open and close my Scan and Pay QR code it is changing each time whereas my Reward only card (in Apple Wallet) is static. Must be due to security.
I had the black background issue at concerts for years but I haven't had that problem in the last 2 years.