i like Nobara (basically Fedora with Nvidia drivers out of the box). Compare the looks and workflow of Desktop Environments (Gnome, Kde, etc) to see which fits best for you. To install, watch a yt tutorial.

Signal is great, but it is centralized. Session messenger is a great example of decentralizes e2ee messaging.

telegram doesnt encrypt by default, its a hidden feature. i wouldnt be too sure about iMessage, i believe E2EE is a bare minimum for everyone.