Cinnamon is hands down my favourite DE. I always see people talking about GNOME and KDE, to me Cinnamon is the best of both worlds. Strongly recommend it with the Orchis GTK theme, which is made for GNOME but works fine on Cinnamon.
My favourite graphical app in the more traditional sense is Firefox. If CLI apps are allowed, I'm a big fan of GNU Nano, a CLI-based minimalistic editor, basically Emacs Lite.
Allegedly the former. By "allegedly", I mean that Telegram is definitely uncooperative in moderation of illegal content, the alleged part is that that is the motivation behind the arrest. I also read somewhere that he was accused of tapping into Macron's manager's communications, but I can't find the article and I don't know how reliable that statement is.