Zorin OS 16 Pro won't boot on Macbook pro

Hi
I have recently purchased Zorin OS 16 Pro but it won't show up on my MacBook's boot screen when I hold down the option/alt key, however Zorin OS 16 Core shows up and boots fine without any issues.
I'm using MacBook Pro late 2011
What is causing this? and can I upgrade from core to Pro from inside the OS?

Have you tried using rEFInd to install Zorin OS Pro?

It sure seems like the 2011 model of Macbook shows up on the forum a lot. I wonder what it is about that particular year... Do macbooks only get produced during a certain year?

@Aravisian thanks for your reply.
No I haven't I'll try and see what happens.

Hahaha I don't know, but this model is still perfectly functional and powerful even for today's standards.