I had a similar issue when plugged to a Samsung TV by VGA cable, it wasn't showing my laptop screen because the resolution wasn't fitting the TV one so I just changed to a lower resolution. Sometimes we just have to change some related settings in the computer or those of the external screen to solve it in no time. Do you see any warning on the external screen when you plug the computer?
Secure boot is enabled. Disabling it can create serious security & instability issues with the Windows OS, so I didn't disable it.
I checked the BIOS, but couldn't find any settings to disable the integrated video card.
I went through the link, but currently, I am looking for an out-of-the-box solution.
The external display works only if I boot through USB disk and select the "Try" option. If the external display is working without installing Zorin OS, then it should very much work after installing Zorin OS.
Right from my childhood days, I was eager to learn Linux OS but in a user-friendly and easy to understand manner. But I never had that opportunity. I thought I could do it with Zorin OS, but that too didn't work.
Unfortunately, for now, I have removed the OS from my laptop.
This may be your mileage, but shouldn't be. The only thing secure boot does is check that drivers are signed by M$. Windows does a similar check before any driver installation. So I don't see how this effects Windows at all, other than a complaint dialog box that it's not enabled.
Any update, usually ones that concern the bios, automatically reenable it, but unless you are making driver updates in zorin, this doesn't usually effect Zorin either.