Right Mouse Button click -- why not just say right-click? (What else is there to right-click other than a mouse button?) It would save us feeble-brained reader the time to look up what RMB means.
For those with the context menu choice, you've had to add that manually to your Windows install at some point in the past. It's not a routine part of Windows. (At least not in a retail version of Windows 10 Pro.)
Perhaps at some point you followed instructions like: