If you want real hacker comms and not larping, then use Matrix via
Element, Signal, or GPG encrypted messages. Otherwise use IRC in a terminal with monochrome
coloring and Gohu fonts for maximum aesthetic, you can prolly use
weechat or something.
You also got Session, qTox, Briar, Cwtch, and IRC + OTR.
Otherwise not sure if you are going to find what you are looking for. Voice+Video communication apps are many, but most of them are absolute garbage.