That is only possible when you really are the owner. And the amount of device out there in the world where people really are the owner is rather small. (Just the Linux desktops and the GrapheneOS smartphones, etc.)
So google's tap to pay doesn't work, but others do, like garmin pay. Random bank apps are hit and miss.
Right, that's the problem, in my opinion. I'm not referring to the apps that require Google's keys only, I'm referring to the ones that allow GrapheneOS keys too. If you use one of these apps, you can use vanilla GrapheneOS builds, but you cannot run your own self-signed builds.
You are gaining freedom relative to running Google's OS, but you are still not free to further modify the software running on your own device.
Apps that require "integrity" should monitor their own integrity only, they should not attempt to infer the integrity of their environment.