Adobe Xd has chosen a hamburger menu for Windows 10 instead of the horizontal menu bar.
And you will be able to mask by right clicking on the selected items and then clicking on the "mask with shape" option (make sure you select the item along with the shape you want to mask it with) .
Hope it helps.
I'm using Windows 10. Even when I select both items (too-large photo that needs cropping + rectangle I drew over the artboard shape for IphoneX) NO OPTION FOR MASK WITH SHAPE EVER APPEARS. The shortcut shift+ctl+M also fails. Please advise me on how to simply crop an image to fit artboard. Thanks.