Add a OneDrive plan to the Office 365 A5 license, so that SharePoint does not need to be assigned for Office Online.
“To assign a license that contains Office Online for Education, you must also assign one of the following service plans: OneDrive for Business (Plan 1), SharePoint Plan 2 for EDU, SharePoint Plan 1 for EDU.”
With A1/ProPlus, we used to assign the OneDrive Plan 1 to a to meet this requirement, and not give SharePoint access, but that is not an option in E5/A5. We do not want a large portion of our accounts in our multidomain tenant to see sharepoint, so we never gave them a sharepoint license. Now with A5, there is no alternative but to give SharePoint plan for Office Online to work.
If there is a way to get the OneDrive Plan 1 license option back (added into A5), that would reduce the needed SharePoint administration greatly.