Same issue here, except the problem first started happening after updating to NoMachine 6.13.1 on macOS and 6.12.3 on Windows. It hasn’t gone away after updating to 7.0.211 on both OS, though mouse pointer dragging did work correctly for a minute or two after updating.
I’m running macOS 11.1 and Windows 10 Education Version 1909, OS Build 18363.1316