My `~/.var/app` directory is 14 GiB in size, 12 GiB of which is used by Signal (...

My `~/.var/app` directory is 14 GiB in size, 12 GiB of which is used by Signal (which is mostly photos and videos) and 1.8 GiB by Firefox. All other programs only take up a few MiB of space.

In terms of installation size it's not a problem either, as one can verify using `flatpak list --columns=size,name`:

    1.3 MB    Flatseal
    2.9 MB    Extension Manager
    47.7 MB   Celluloid
    604.6 MB  Freedesktop Platform
    680.0 MB  Freedesktop Platform
    533.8 MB  Mesa
    533.8 MB  Mesa (Extra)
    469.8 MB  Mesa
    469.8 MB  Mesa (Extra)
    46.9 MB   Intel VAAPI driver
    50.9 MB   Intel VAAPI driver
    20.3 MB   FFmpeg extension with extra codecs
    790.0 kB  openh264
    763.9 kB  openh264
    243.7 MB  GNU Image Manipulation Program
    7.7 MB    HEIC
    17.6 MB   Characters
    14.2 MB   Connections
    25.4 MB   Image Viewer
    946.7 kB  HEIC
    25.5 MB   Sushi
    39.8 MB   Papers
    941.3 MB  GNOME Application Platform version 46
    1.0 GB    GNOME Application Platform version 47
    794.1 kB  Fonts
    137.7 MB  gThumb Image Viewer
    1.1 MB    adw-gtk3 Gtk Theme
    269.6 MB  Firefox
    482.3 MB  Signal Desktop

The duplicate entries is because certain Flatpaks may require different versions of e.g. the Freedesktop platform (that being possible is one of its big selling points).

In short, storage isn't a problem at all for any computer produced in the last 20 years.