I would like to make some edits on this edge. I.e cut extrusion. In order to do so I suppose I would have to make a plane perpendicular to it. How can I?
Its a curve/spline. You can't really 'sketch' on it.
Sketch need to start on flat surface.
You can sketch on the flat face.
You can create a plane perpendicular to the spline but you need to add/pick a point on the spline.
It looks like you have a flat surface already (see the red star below). If it is flat, then you can sketch directly on it. If it isn't flat you can just use a 3d sketch.
it depends on the cut you want to make, what were you trying to make, something like a chamfer?
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