I am trying to use a 3rd party external GPU enclosure that attaches via thunderbolt, and when attached, I got the message pop-up that external GPU support was not enabled by the vendor, and as such the device will likely not work? Has Dell locked the Latitude 7480 down to no external GPU support?
Probably. I read somewhere that since Dell is pushing their Alienware external GPU stuff that uses a proprietary connection, they never enabled external GPU support via Thunderbolt.
For what it's worth, the Akitio Node GPU enclosure recently received firmware that allows it to operate even with systems that say they do not support external GPUs as long as the Thunderbolt firmware on the system is NVM 18 or newer, and the 7480 just recently got Thunderbolt firmware available that's newer than this.
I'm not sure what it takes for the system to be recognized as "officially" supporting external GPUs and why Dell systems claim they don't. One possibility is that Dell just doesn't want to deal with issues created by customers not understanding that they can't hot-unplug a GPU enclosure the way they can with most other Thunderbolt 3 devices like dongles and docks.