Grr, I hate that One Drive, first thing I deleted from new laptop. It works for some people, but not me. Anyhooo...
ESO wants to look at a subdirectory of My Documents for the addons. So, at some point you moved, or one drive moved them for you, My Documents to the One drive. Well, that ain't gonna work as it's a cloud drive.
So, the quick and easy answer is to move the location of My Documents back to your machine. You can do that in the Properties of the My Documents folder.
https://support.microsoft.com/en-us/help/253682/how-to-change-the-default-location-of-the-my-documents-folder
From all the research I have done I don't think it is possible to move the Addon's directory from the My Documents Hierarchy with the game itself. There are NTFS Joins and Redirects you could do, but not sure how successful they are for this purpose.
Googling that error lead me here. https://support.microsoft.com/en-us/help/2936105/operation-to-change-a-personal-folder-location-fails-in-windows
Tried that, got this error: "Folder Can't be moved here. Can't move the folder because there is a folder in the same location that can't be redirected. Access is denied."