Actually, I'm using Microsoft 365.
How do I backup to Onedrive. I'm syncing files, but a number of sites refer to Onedrive b/u and I can find sw purporting to backup to Onedrive. I'm unable to find how to backup.

Many way are available to backup to Onedrive , you can use the Onedrive agent , Robocopy , Goodsync , Gs Richcopy360 , Syncback ....etc .
It depends on what kind of data , amount , and if you prefer CLI or GUI backup way