English Translation
I want to know what this is all about.
This is all I could find (in the main dictionaries) where retourner de quoi means to be about:
retourner
verbe impersonnel
peut-on savoir de quoi il retourne ? = what is it all about?, what exactly is going on?
© Larousse 2014
De quoi il retourne : de quoi il est question.
« Savez-vous de quoi il retourne ? dit-il à Julien »
© Le Petit Robert 2025
(Translation by Reverso:)
What it is about: what it is about.
« Do you know what this is about? he said to Julien.