Just the same error on macOS, for any API I connect to. Just the message on the Xcode debug console, because the GET succeeds.
nwresolverstartquerytimerblockinvoke [Cxx] Query fired: did not receive all answers in time for ***
MultiPlatform application, macOS Big Sur Beta (same behavior anyhow on Catalina as well), iOS 13.5: on iOS no problem, while the error is 100% systematic on macOS.
On macOS I cannot register for CloudKit push notifications as well: I wonder if the two issues are correlated (again: no problem with push notifications in iOS)