Hi @Elizabeth,
You'll need to set Full Control add-in permissions at the Web scope. The site collection scope url should be http://sharepoint/content/sitecollection
Read this article for more:
https://learn.microsoft.com/en-us/sharepoint/dev/solution-guidance/security-apponly-azureacs
https://learn.microsoft.com/en-us/sharepoint/dev/sp-add-ins/add-in-permissions-in-sharepoint
The xml in your case should be like following
<AppPermissionRequests AllowAppOnlyPolicy="true">
<AppPermissionRequest Scope="http://sharepoint/content/sitecollection"
Right="FullControl" />
</AppPermissionRequests>
This document shows how to break role assignment
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