Hi Moi3dFan,

I had the same question a while ago, but after playing around with it I realized that this is a fact of geometry rather than a software limitation. It's not possible in general to draw a circular arc tangent to any 2 curves that aren't in a plane. You can try this out with "Draw curve" > Arc > Tan and you'll find that in many cases there's just no way to do it.

The curve that you're ending up with there at the end is not a circular arc.

But, to do this kind of thing you can trim the curves away from the corner a bit, select them both, and then do Construct > Blend.

- Peer