My advice is try using existing documents with Libre office. You can install it on windows as well.
I use Linux for over twenty years now and installed windows on a vm last week to Wirte my resume. Libre office is fine, you run into problems when opening and editing existing ms office documents. At least that is my experience.
But give Libre office on windows a shot, see if you like it.
The fact that the ccc uses matrix as their official chat “app” doesn’t imply that it is inherently insecure I would say.