Flickering pixels (snowstorm type effect) on 2nd screen after update 8/10/21

[newbiemacuser84]

Hi all

First post on here but thought I would ask your advice. I have recently updated my Mac to Big Sur 11.6 and started the Mac this morning and noticed that the 2nd screen (linked by Dongle and HDMI) now has a flickering pixel issue which wasn't there yesterday and very occasionally flickers on and then off and back again (1 second delay-ish)

This wasn't happening yesterday before the update and is making the second screen difficult to use. I have tried the following remedies so far:

1. Restarted the Mac
2. Unplugged everything and reinserted
3. Checked if there are any other updates (which there aren't)
4. Monitor seems fine with alternate input (PS5)

Any advise would be greatly appreciated

Thanks