Chamfers can be done by extruding the chamfer shape along a wireframe of the geometry to be chamfered, then subtracting the extrusion from the original geometry. I'm not sure how I'd do fillets in OpenSCAD, though.
You can use a Minkowski sum to give yourself a fillet. I did it once. It worked but was 2x as hard as learning enough Fusion360 to do that whole part and then each design after that is 20% as hard.
I eventually got pretty good at OpenSCAD, but I’d say I now reach for OpenSCAD about 3x/year and everything else is in Fusion.
I either live without, or get creative with use of hull, cylinder (including cones), making toroids by radial extruding circles (using the toroid as a cut shape just to get a fillet around a post), or I just open the scad file in freecad, and then apply the fillets in freecad.
It's definitely a weakness in the sales pitch having to work that hard for something you want that often.
I eventually got pretty good at OpenSCAD, but I’d say I now reach for OpenSCAD about 3x/year and everything else is in Fusion.
I wish I’d have switched years ago.