highradio Thanks for the response. Just a couple of things to bear in mind is that from many years of experience we know that everyone is different, so some of your points may not apply to some.
For example, many people do in fact have dithering issues with Nvidia / AMD graphics cards on desktop computers that use no Intel graphics. And the same thing with the PS4 / Xbox One. This became a problem around the same time that LED screens became prevalent, and different colour settings in the Nvidia control panel have been proven to trigger problematic temporal dithering by @Seagull and others.
Some monitors themselves seem to be involved in the dithering process also. And also something I've noted is that 'G-Sync Enabled' laptops are often referring to the fact they can connect to G-Sync monitors, and not necessarily that the laptop display itself is connected via G-Sync directly to the Nvidia card. I'd be interested in whether this means that the laptop display still uses the Intel drivers?
That's amazing that the first laptop you tried worked for you but there are many variables involved in the hardware alone, before you even start thinking about different brains...! This is why I thought it would be good to try a 'known-good' setup first, so thanks for the model number.