As you may have noticed, the Librem phone and other Linux phones don’t always have the same apps you may be looking for for iOS and Android, with few available within the built in store. While you must check with developers and encourage them to build their apps for Librem phone, there are a number of these that can be installed already from Flathub/Snap store:
The instructions for installing Snap store on Debian/Linux are here:
sudo apt update sudo apt install snapd sudo snap install core sudo snap install snap-store
After running those three you should have the Snap Store icon.
Selecting it from the app drawer, you should be able to browse most of the Snapcraft store.
However, note that the arm64 architecture of the Librem – and other similar mobile devices, may reduce compatibility. The app must have a build for arm64 for download. If so, it should install and run from the app drawer like other phone apps.
Flatpak is another common way of installing apps that is fairly common – you can install the repository with the download here, and view some traditionally-desktop apps by selecting “show incompatible apps” in the PureOS Store preferences. Some apps such as Viking will now let you choose the source in the top right, and the Flatpak apps can be more up-to-date than the Debian standard old versions.
Another issue you may note is apps that go off the screen a bit or require changing screen orientation. In this case you can contact the developer and report a bug – Linux apps are going to be needing a restructuring now in a similar way as has happened on websites for phone-responsive designs when smart phones first became widespread.