Thanks all for your replies. I figured out the solution and just wanted post incase anyone else comes across this issue.
I purchased a 2016 GT350 with 1,000 miles on it. The owner rarely drove it and never bothered to update Sync to the latest firmware.
The issue was actually caused when updating Sync 3 from version 1.0 to 3.0, which apparently can’t be done. You must first install an intermediate version such as 2.2, the files for which can be found on various forums. You can then update to version 3.0. The USB hub i purchased from my dealer now launches Apple CarPlay.