Purism contributed with the creation of
libhandy a library with adaptive GTK3 widgets that can be used to make a GTK3 application adaptive.
There is work to port
libhandy to GTK4. This was creating a tool to allow adaptive GNOME apps, along with developer documentation on how to make your appliaction adaptive. And also promoting libhandy.
This created the tools for many GNOME application developers to make their apps adaptive.
Besides that Purism contributed to making what would be the base (as in ready on day one) GNOME applications for the Librem 5: Mail client (Geary), Browser (Epihany), Clock (GNOME Clocks), Address book (GNOME Contacts), also a calls application and a Chat/SMS application.
Several Purism developers are also GNOME developers. Every single GNOME app developer that ever asked a question about making his app adaptive in our channels got a reply.
You can see here a non exhaustive list of working apps: https://tracker.pureos.net/w/pureos/mobile_optimized_apps/