I have this edge I am trying to cut

Its protruding out but is really fine and hard to boolean difference out with another shape please help

Hi Lukas -
Use ExtractSrf to extract and then delete the surfaces that you don’t need. Then extract the side surface and scale that 1D to its correct width and use that to trim the bottom and top surfaces. Join all.

It might be a good test for the InfinitePlane tool -

Start BooleanSplit. Select you object as the object to split. At the prompt for the cutting object, type in ‘IP’ and enter. Select the larger vertical face - the one you want to keep, as the cutter. Enter.

Does that split off the little bit? If so, delete this small bit and MergeAllCoplanarFaces on the result.