Hi Paul,
Thanks for the link. I read through it and it put me on the right track. I have it solved.
I have two monitors - ancient Acer monitors, identical, each 1920x1080, so it definitely is not a 4k/8k issue. Back when I bought them they were decently mid to high specification.
I have an Asus ROG gaming laptop with two graphics adapters.
Looking through the display settings, I see that one of the monitors is connected to the AMD Radeon graphics while the other is connected to the NVIDIA RTX 3070. All I had to do was move the map view window from the AMD monitor to the NVIDIA monitor, and now it's working. I guess it's time to upgrade to a single wide monitor and just run it off of the RTX 3070.
Thank you for the help, and thanks to the wonderful team at dGB for making a free version of OpenDtect.
Cheers,
Mike