Error: This app can not be enabled because it makes the server unstable
NextCloud version 13.0.1 (stable) gives the above error and won't install SharePoint Backend.
Please provide the information according to the issue template: https://github.com/nextcloud/sharepoint/blob/master/issue_template.md
Hello, I encountered this very same issue with a fresh nextcloud 13.0.5 snap install, but found the fix to be enabling "External storage support" first and then enabling the sharepoint app.
@goosemaster indeed external storage support is a dependency
Saw a similar issue myself with the Dropbox backend for NexCloud. Just had to enable external storage within NC before configuring any add-ons.