Installing Fontra Pak on your computer
Fontra can be installed locally using Fontra Pak, a self-contained application which allows you to edit local files in your browser using Fontra. The installer is available only for macOS and Windows. Linux users can build Fontra from source or if in X86_64 platform has option to download pre-compiled pyinstaller binary or install snap package as per this instructions or install the flatpak version as per their preference.
Have fun: Building Fontra from source