Debian / Ubuntu apt mirror — GUI and terminal builds over I2P.
If this site is empty or KEY.gpg 404s, no mirror is published yet — install .deb from GitHub Releases instead. When live: deb822 .sources, then i2pchat / i2pchat-tui (amd64; arm64 when the mirror lists binary-arm64).
Use Architectures: amd64 arm64 in your .sources if the mirror ships both (see links above). If binary-arm64 is missing, install *_arm64.deb from GitHub Releases.