In order for the user to have access to Linked record data between different solutions the user has to have permissions for both solutions. This is a problem as the user would have access to view all data in both solutions. Another problem is that because there is no permissions between the solutions Linked Records across solutions cannot be viewed in FillOut.

With permissions between solutions user with access to Solution A should be able to pull up data in linked records to Solution B without user access to Solution B. Also FillOut should be able to be connected to Solution A but have access to Linked Records to Solutions B in Solution A