I have played with this backend tool a little bit. My windows beta installation included the async bug CommandLine upload to GoogleDrive throws ObjectDisposedException · Issue #4556 · duplicati/duplicati · GitHub, that is why I downloaded the source and rather built myself. Kudos to the team the building was refreshingly easy, I was expecting thousands of warnings and caveats and was positively surprised. The locally built backend tool does the job just fine.
However I did not want to implement retrying, backoff, check-if-it-is-still-there, etc mechanisms and decided to go another route: the real root cause behind my earlier decision of doing the initial backup locally was due to the uncontrollable network throttling. I have a 400Mbps/96Mbps connection and during video conferences (WFH) my colleagues were tearing my head off for having such a bad connection. So I went now and found others also had issues with network throttling in general:
But it seems resolved in the version I am using(2.0.6.3_beta_2021-06-17): --throttle-download ignored, --throttle-upload throttles download too · Issue #4115 · duplicati/duplicati · GitHub
So I went ahead, set asynchronous-concurrent-upload-limit to 1 and throttle-upload to 8 MBps, restarted the backup configs and according to speedtests it looks fine, crossing my fingers for the confcalls. 
Anyways for the initial full backups which I estimate to run for 7-9 days starting from now I need to take the daily 750GB gdrive limit, so I could not move much faster. Once the initial backups are done, I will switch to nightly scheduled ones and YOLO no throttling.