Hi @JR_482
Via searching online, if TLS 1.2 is not enabled, you may get such error message.
Besides, please make sure connection between your Windows server and a WebDAV drive works properly. Here is a link you may have a look: https://nerdia.net/2016/03/26/connecting-a-windows-client-to-a-webdav-drive/
(Please Note: Since the web site is not hosted by Microsoft, the link may changed without notice. Microsoft does not guarantee the accuracy of this information.)
If this protocol has been enabled, I suggest you open a ticket with Microsoft Support to help review your issue and help you test remotely. Microsoft support may collect Office logs and use Ping and Telnet to this WebDav drive.
Thanks for your understanding.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.