For all who aren´t able to add a credit card to Google Wallet with rooted devices on C.20. It works with Magisk if you:
1. install modules safetynet-fix and hide-props-config (latest versions)
2. set magisk hide and enable zygisk
3. force deny list check Google Play, Google Play Services, Google Wallet
4. open a terminal app (I used termux with command "su") and type in "props"
5. be patient until props shows its alternatives, then choose fingerprint of "Google 6 Pro" and set this as the default one
6. delete complete data of above mentioned Google apps
7. reboot and check in Google Playstore if device is shown as "certified" or latest Google Play Update is shown
8. optional check safetynet status with Yasnac etc.
But you should be good from this on. You can use Google Wallet as expected. I did a factory reset before the process, but I´m not sure if this is necessary.