HI wim,

re:
> how can I finish this lofted open shape, so that the end is smooth and round and has no
> visible division line, so that it looks like one continuous smooth object?

It's hard to give good advice just looking at a screenshot, can you please post the .3dm model file with the objects you show there?

Probably the first thing I would try would be to use Rail Revolve to make the rounded end and then have some empty space between that rounded tip and the main part and then use Construct > Blend to put in a smooth blend surface.

Or another possibility is to cut the end edge in half and then use Blend between the 2 halves.

Also using Loft with Loft style = "Loose" and ending in a point can be good, an example:
https://moi3d.com/forum/index.php?webtag=MOI&msg=6082.8

- Michael