/users does not return Service Accounts, folders/0/items does not work for Service Accounts userId

Using an App+Enterprise JWT (server Auth) Service Account I am unable to interact with other service accounts using the Box API.

/users - return only users not service accounts
/folders/0/items - returns 403 when I am impersonating (As-User) a Service Account userId.

The issue is that I am trying to find all files in the organization, and service accounts can hold files/folders under their file tree, but these are unreachable using the API.

Is there any way to find service Accounts and read their files using the API?