Yes I noticed that, but really i'm in love with Quanta for the way you can edit CSS

I think its the only KDE app I use on my system, I'm sure i've tried out something else over the months but i dont remember now. I've tried KDE too but I feel GNOME has a more solid performance

Thanks to everyone who answered me!

This is perhaps a bit anticlimactic, but....

There's maybe a subtle distinction to be made between "KDE vs. Gnome" and "Qt vs. Gtk". For example, is Quanta a "KDE app", or is it a "Qt app"?

When we say "mixing desktop environments", it really means having both Qt and Gtk installed---plus some intermediate libraries, utilities, etc. Other that using disk space, I can't see any intrinsic harm in having both installed.

The only thing that slows down a computer is what is actually running.

Well, some would say that stopping to use a program that works very well for you just because the look and the file dialog is a nonsense.

It's about tastes.

It's a kde app, since it links to kdelibs, and not just raw qt.

But it's true that, besides disk space, there's no downside. So, I use whatever fits me. Note that if look is all that bothers you, you can always use qtcurve, which is widget style that works for both qt and gtk (gnome and kde), so the applications will look consistently. There's little you can do about the file dialogs (that I know of) though. I know about kgtk, but it's an ugly hack, and besides that it converts the gtk dialogs to kde ones, and not the other way around.