Sorry to hear you are having issues. I tested the 4K Moon river and can't reproduce your issue on my system. Perhaps try changing these 3 setting and see if any of these setting work for you.
It’s still not very clear, so just to confirm, the issue remains the same even after you tried all three settings, correct?
If so, please try, uninstall Deskscapes 2026, reboot immediately (important), download latest version available in your account product download page: https://store.stardock.com/myaccount/products. Install it, reboot immediately again. Retest it and report back.