You will find many opinions about managing your images. A couple of links-
Using Collections- Workflow smart collections – Lightroom Solutions
I have thought weeks about it and just after posting my question I have found a solution that works for me: Stacking -> Collapse All Stacks only shows (and exports) the top image from the stack.
If I create a virtual copy of an image (e.g. for a bw conversion) I need to remove this from the stack if I want it to be expoerted later.
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And a nice answer to your own question "Stacking"
If you will only want the B&W version exported, you can make it the top of the stack so it shows in grid view.
(Expand the stack, Right-click the B&W > Stacking > Move to top of stack.)
Thank you very much, that's a great idea.