I’ve tried several techniques, but I’m sure it’s inexperience here.
The last thing I tried was taking the 2D drawing and extruding it. Then I try to round over the top like it is on my car with a chamfer, and it tells me “the edge has no blend.” (Try telling that to U2.)
I would suggest to create a fillet instead of a chamfer -it is more tolerant to geometry- and then tune the shape of the fillet to be as close as possible to a chamfer (ensure the slider stays blue, not red)