Hi, i want to make a smooth boolean between the X form and the "prongs" sticking out of it. I tried union and a clean up, i also tried offset cut but both did not make it smooth, bevel does not do antything...
You should better redo it: First in Edit mode select all and CtrlE > Un-Subdivide to simplify the topology (tweak the parameter in the Operator Box, you can even simplify more), select 8 faces:
Inset i then right click > LoopTools > Circle (you need to enable the LoopTools addon):
Extrude up, fill the top faces with F:
Bevel the top and bevel the bottom (CtrlB):
Give it a Subdivision Surface modifier: