I am using QGIS 3.8.1 on Mac and trying to create new Polygon in this step. However it does not work.
In my case, at least, I worked out that it depends on whether my cursor (ready for the next click to create the next point in the line or polygon) is hovering over any map feature in any level that it could snap to. If so, a hover text should appear by your cursor showing the name of that feature. Right-clicking doesn’t work when this is the case. But just move your cursor away to any blank space on the map where there is no feature that it wants to snap to, and then right-click, and it should work. (The usual dialogue box should pop up for you to enter the ID for your newly completed line or polygon.)