A few years ago I got 5 of my millennial friends to move from FB Messenger to Telegram and it took some peer pressure from me and essentially one hangout where we were all together, and moved in one go. Telegram is not perfect but overall it’s much better than being on FB messenger.
On KDE there’s System Monitor, which you can customize to show graphs for CPU usage and temp, among other things, and GPU usage and temp too.
For in-game monitoring there’s Mangohud, also very customizable on what you can show in the overlay