I updated to Cura 4.2.1 and have been problem with my Surface getting very laggy with the bluetooth mouse I use. Intermittent pauses and lags in updating the pointer position - sometimes so bad it's unusable. And also when Cura is just in the background, too.
Going to a wired mouse fixes the problem.
I didn't have this trouble with earlier versions of Cura.
I'm now running in Win8 mode to avoid the launch and crash problem, but the lag with Bluetooth mouse happens both Win8 and Win10 compatibility modes.