Application development for the Librem 5 is not tied to a particular set of technologies. However, for simplicity, we recommend that you use the same set of tools and libraries that the Librem 5 developers have used.
The default development environment is based on the GNOME software stack to match the software provided on the phone itself. Users who have installed Plasma Mobile as their preferred environment may wish to use tools from the KDE project instead.
Where appropriate you can use the versions of these that are provided with your operating system. However, it may be necessary to install more up-to-date versions of some tools when new features are needed. The preferred method for doing this is to use Flatpak to install sandboxed versions of the required applications.
Once you have set up the development tools for your workstation, you can start exploring Application Development for the Librem 5.