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After more than a year of struggling with this issue and striking out with both Microsoft Office and OneDrive support techs...I was relieved to discover Mac Wheeler's resolution to this issue
(https://www.macwheeler.com/windows-10-office-365-cannot-connect-over-openvpn-fixed/). Assigning a default gateway address to the IPV4 protocol works like a charm! I used 198.162.1.1 and it immediately resolved the issue.
I have wasted many hours of time with MS Office support techs who were absolutely clueless. OneDrive support is not reachable by phone and they too are clueless; point the finger at their Office support colleagues. It is amazing to me that the Sr. Software
Engineer I last spoke with at Microsoft was completely unaware of the issue and any solution for it. It causes one to ponder how internally fragmented the MS organization might be. Frankly, it ought to be a bit embarrassing that Microsoft has allowed this
issue to cause so many users so many problems for so many years.
By the way, Office365/OneDrive connectivity through a VPN has never been an issue for iOS MacBook.