Platonists beginning in the Old Academy itself and up to and including Plotinus struggled to understand and articulate the relation between Plato's Demiurge and the Living Animal which served as the model for creation.
The central question is whether "contents" of the Living Animal, the Forms, are internal to the mind of the Demiurge or external and independent.
For Plotinus, the solution depends heavily on how the Intellect that is the Demiurge and the Forms or intelligibles are to be understood in relation to the first principle of all, the One or the Good.
The treatise V.5  sets out the case for the internality of Forms and argues for the necessary existence of an absolutely simple and transcendent first principle of all, the One or the Good.
Not only Intellect and the Forms, but everything else depends on this principle for their being.