Read https://github.com/shiftkey/desktop/

wget -qO - https://mirror.mwt.me/shiftkey-desktop/gpgkey | gpg --dearmor | sudo tee /usr/share/keyrings/mwt-desktop.gpg > /dev/null
sudo sh -c 'echo "deb [arch=amd64 signed-by=/usr/share/keyrings/mwt-desktop.gpg] https://mirror.mwt.me/shiftkey-desktop/deb/ any main" > /etc/apt/sources.list.d/mwt-desktop.list'

sudo apt update && sudo apt install github-desktop