adjustment brush stops at the edge on lightroom

The cursor stops at the edge of the photo and the brush does not move onto the photo...I can not use the brush on the photo. I cannot use the brush at all...once I move the cursor to the edge of the photo it does not move and the circle does not appear.

"totally useless"? overstating things, I think. AFAICT the brush does not quite stop at the edge of the photo, by the way: it continues beyond the edge of the photo by a distance of the current brush diameter including feather. So you can still place any mark that is going to be visible.

Furthermore if you move the whole brush mask 'layer' to the left, you can now paint more brush strokes right-of-picture, onto a part of the mask "canvas" that was formerly out of view. And on moving the brush mask 'layer' around further, an area of brush marks larger than the picture area will now be seen to have accumulated. I can't think of any use case for doing this, but there it is.

The brush tool can only be a brush within the image area. When you move the brush outside of the image area it becomes a cursor. The same applies to the zoom tool, heal tools, etc.

Please describe the behaviour you expect to see and why you think such behaviour would be useful.