Only me? I run into this constantly and have no idea what I’m doing wrong. Maybe the shape is too complex? I can subtract a cylinder from the same face.
Hello! When you are working with the Boolean tools, please make sure to have a clear intersection between the bodies and try to avoid surfaces that are tangent with each other. In this case, please draw a rectangle that covers the filleted cutout shape (or it may be bigger a bit) and select that cross-section also for the extrusion.
Another suggestion. Create a plane that’s offset a little bit back from the cut you’re trying to make and project your cutting tool onto there, then extrude that into your shape. I find shaprs subtract tool tends to work a lot more happily when it has a little bit of a running start to work with for odd cuts. Might not work, but worth a shot