Welcome to another installment of installing Firestorm Viewer on Linux.
I use Mint 21.2, 21.xx should be the same.
Open a terminal. N often works.
Download the latest version from Firestorm Https://firestormviewer.org/download/
Dowload this to your /home/Download directory.
Then in the terminal
CD ~/Download/
tar -xvf Phoenix*.tar.xz
cd Phoenix*
sudo ./setup.sh
Then you will be prompted to pick an installation directory, which defaults to /opt/firestorm. I use /opt/fire
Next run the firestorm viewer
cd /opt/fire
sudo ./firestorm