Not sure if this in the right place, since I don't actually know if it's a GPU issue or not.

I have an Acer Nitro 5, model AN515-54, and I'm trying to use it with an external monitor and the laptop screen serving to extend the display. The monitor and the laptop display have the same native resolution (1920x1080), refresh rate (60Hz), and colour settings (RGB). I'm using the Windows-recommended scaling for each (125% for the laptop screen, 100% for the monitor).

The setup mostly works well, except for problems with ClearType. Whichever display I've set as the main one determines the ClearType settings for both. In other words, the appearance of text on the secondary display changes as I calibrate ClearType for the primary one, but does not respond when I calibrate the monitor on which it's actually displayed. ClearType settings for the main display (whether it's the laptop screen or the external monitor) are applied across the board. As you can imagine, this is frustrating as the displays use different values for scaling - it means I have to pick one of my monitors to be "the blurry one".

Strangely enough, no other calibration settings are affected - for instance, I can independently control the colour balance of each. I've also verified that it has nothing to do with the external display itself (the problem persisted with a different monitor), the scaling (setting the laptop to 100% for consistency with the external monitor didn't help), or any drivers (problem persisted before and after updating drivers for all monitors, as well as the Intel UHD and NVIDIA GeForce cards).

This may be a problem in Windows itself, but I also wonder if it has something to do with the GPU's. The laptop display is connected to the internal Intel GPU, but the HDMI port is connected to the discrete NVIDIA card. When I click "Identify displays" in the NVIDIA Control Panel, the number 1 appears on both monitors (although Windows itself correctly identifies them separately). Also, the laptop display disappears from the PhysX configuration when I plug in the external monitor. I'm wondering if the GeForce is somehow treating them as parts of the "same" display, and if this behaviour is somehow influencing that of ClearType?

Any help is greatly appreciated - I've been Googling like crazy, and haven't found anything about this specific issue (beyond re-installing the drivers).

For reference, I am running Windows 10 version 1809.