Please exit any apps that might be drawing over the screen. Google Pay problem solved for any phone!
As a Poco f1 user, this gpay drawing over the screen issue was sorted by enabling the notch instead of my preferred setting of hiding the notch, works for Poco F1 and Redmi Note 9 Pro Max!
To summarize, disabling "Hide notch", if it didn't work, disable quick ball feature and if that also didn't work, disable app access which has "Draw over screen" Permission.
Finally, if you see GPay app update, as Google is working to resolve this, that update itself will automatically resolve this bug.