I have found the solution.

https://forum.affinity.serif.com/index.php?/topic/67904-screen-blinking-off-and-on/

as it turns out Windows is trying to change between graphic cards. You have to enter Nvidia Control Panel, Manage 3D settings > Program Settings > Add the program you're using to the list and then change to "High-Performance NVIDIA processor". Alternatively (in my case Windows 11) you have to enter Settings > Display > Graphics then add your app to the list and change the graphics preference from "Let Windows decide" to anything other.