Playing around with the preliminary version of the Librem 5 in the qemu virtual machine, there is a huge amount of Debian->PureOS software available to be installed. I have been able to install every GTK program that I wanted.
The problem is that very few programs are designed to fit in the tiny screen and their code will have to be adjusted to work with Libhandy.
I just tried VLC and I can only see the center menus but not the menus on the edges. Rotating horizontally makes some of the software usable, but Phosh needs to add scroll bars for when a dialog box is bigger than the screen.