On MacOs it seems that a mouse drag is not possible when switching from a screen to an other, a mouse click is needed first when moving to an other screen so the drag can work.
example : RDP full screen on all monitors, all the monitors showing the desktop. drag a selection square on the desktop of one monitor, this work, move the mouse to an other monitor, try to do them same (drag a selection square on the desktop), this do not work, you need to do a click in the monitor before so the drag work. this is really annoying when working on several software where often have do to drag selection and switching from one monitor to an other. I am using RDP since many years with the same configuration and I don't remember having this issue before. let me know if this problem can be fixed on my side or if this is a bug. We are several people with this issue. thanks a lot
Configuration : MacBook Pro, RDP connected to a Windows workstation, 3 monitors.