Top of the morning to you, Theuns,
Thanks for voicing an unasked question of mine . . .
and getting such a good response ( ͡° ͜ʖ ͡°)

Hi Theuns, sure you can do this without any problem. Quite normal thing. You can have several categories and put posts in several of them, plus they appear in blog roll. This is the matter of internal organization. I have posts on 2-3 places, no problem with duplicate/triplicate content.

This all works for posts. But if you add a plugin (I use one) you can have categories for pages as well, and do the same; they will not be in blog roll of course. See this nice tutorial by Labman: Does posting a blog in 2 different categories count as duplication?

I would personally shy away from such practice. Search engines may treat it as duplicate and your ranking suffers.

Good question!

My commons sense says No, you better don't do that, but when I check the internet there seems no problem to do it anyway...

So, I hope you get some good replies, so it also becomes clear to me...

Grtz,
Bert