Hello Hugh,   External GPU should work without too many problems and the only thing to know is that Vectorworks will benefit from a single GPU and it will not be possible to use both, internal and external at the same time.    Please try to follow the steps below to see if this would improve the performance: https://support.apple.com/en-gb/HT208544   After everything is connected I would recommend to contact us directly. Our support email address is uktech@vect