There seems to be an issue with this fix at this time.
I have had to do this on a number of Pixel phones in the past, Pixel 2 and Pixel 4XL. Today I received a warranty replacement for a Pixel 4XL (battery swelling).
Running:
bmgr backupnow --all (fails with transport error)
bmgr backupnow appdata (fails with package missing)
Setting the transport to com.google.android.gms/.backup.BackupTransportService doesn't work.
The only way I can back up data is to remove all device screen locks etc which is not helpful when using google pay.
