Screen refresh rate issue

[littlegreen]

TL;DR
Internal screen drops down to 25 or 30Hz when laptop is connected to an external monitor - "Extend Displays" mode.

Hi,

I don't know if this is a standard issue or not. Admittedly, I rarely attach a third screen to my laptop. I usually reside on Sidecar for a secondary screen.

I had Sidecar running today over USB (yay! Finally!) and connected an additional screen via HDMI.
The screen only has DVI connection, so I was using a DVI-to-HDMI dongle to connect. (I don't think this is an issue, as they're both digital signal connections)

The actual issue I am experiencing though, is not with the external monitor - that works exactly as expected. The issue is with the internal laptop screen - it appears to drop down to some 25-30 Hz. refresh rate. I am not sure exactly how low it goes - but it is MORE than noticeable, especially when I drag windows across screens - or even moving the mouse.

Is there any way to force the internal screen to stay at 60Hz? I am not mirroring the screens, as I need the extra real estate when working.

HP Laptop,
CPU: i5-8250U
Graphics: UHD-620

Clover folder attached.

Many thanks in advance!

 

[littlegreen]

Fun fact:

When no secondary monitor is connected my internal display runs in a 24bit colour mode, as opposed to the 30bit when the external screen is connected.... do I need to declare different colour space in Clover to set that straight?