So I have this rather complex shape now. I managed to combine several shapes into one monochrome shape. Hurray!
But now I found that I did it the opposite way of what I really want.

I'll try to explain.

Basically I have combined two shapes. Let's call them "Shape M" and "Shape C". Shape C is cut out from Shape M which still is massive. This should be the other way around though. The Massive shape M should be what's cut out, while the cut out shape C should be the selectable area.

How do I switch those?

And sorry for asking such rookie questions. I usually use the Help function first and if that doesn't help, I use Google to find the answer. But here, I don't even have a clue how to ask this with a seachable phrase.

I found out this though:

I turned it all into paths. I drew a rectangle around it. Then I chose "Path" > "Exclusion"

And ... tadaaaa!
It works! At first glance, that is.

Now there is a rectangular around the entire thing that should not be there. So I tried to delete the rectangular the only way I can imagine: "Edit Path By Nodes" and removing the four nodes.

Alas, when I do that, the entire thing gets inverted again...

Hmmm... never mind. I first need to check something.

You want a hole in a nothing?... Maybe if you could share a drawing we could help.

As I said, never mind. I first needed to check something.

In the mean time I found out what was wrong. Problem is solved. This thread can be deleted.
Thanks though!