I installed Alt kworkstation 9 x86_64 . After adding Flathub repository [flatpak remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo] I tried to install flatpak applications using Discover but it would quit unexpectedly every time I tried.

The reporting and debugging system did not work when I tried to report the error. I decided to install via terminal but it shows me this:

seba@seba-pc ~]$ flatpak install flathub com.github.tchx84.Flatseal

Note that the directories 

'/var/lib/flatpak/exports/share'
'/home/seba/.local/share/flatpak/exports/share'

are not in the search path set by the XDG_DATA_DIRS
environment variable, so applications installed by
Flatpak may not appear on your desktop until the
session is restarted.

Looking for matches
Required runtime for com.github.tchx84.Flatseal/x86_64/stable (runtime/org.gnome.Platform/x86_64/3.36) found in remote flathub
Do you want to install it? [Y/n]: y

com.github.tchx84.Flatseal permissions:
    ipc                  fallback-x11         wayland      x11      dri
    file access [1]      dbus access [2]

    [1] /var/lib/flatpak/app:ro, ~/.local/share/flatpak/app:ro,
        ~/.local/share/flatpak/overrides:create
    [2] org.gnome.Software


        ID                                      Branch    Op    Remote     Download
        ID                                      Branch    Op    Remote     Download
 1. [|] org.freedesktop.Platform.GL.default     19.08     i     flathub       88.6 MB / 89.1 MB
 2. [ ] org.freedesktop.Platform.openh264       2.0       i     flathub      < 1.5 MB
        ID                                      Branch    Op    Remote     Download
 1. [|] org.freedesktop.Platform.GL.default     19.08     i     flathub       88.6 MB / 89.1 MB
 2. [ ] org.freedesktop.Platform.openh264       2.0       i     flathub      < 1.5 MB
        ID                                      Branch    Op    Remote     Download
 1. [/] org.freedesktop.Platform.GL.default     19.08     i     flathub       88.6 MB / 89.1 MB
 2. [ ] org.freedesktop.Platform.openh264       2.0       i     flathub      < 1.5 MB
 3. [ ] org.gnome.Platform.Locale               3.36      i     flathub    < 323.0 MB (partial)
 4. [ ] org.gnome.Platform                      3.36      i     flathub    < 324.5 MB
 5. [ ] com.github.tchx84.Flatseal              stable    i     flathub    < 699.9 kB

Warning: Could not unmount revokefs-fuse filesystem at /var/tmp/flatpak-cache-CTHFP0/org.freedesktop.Platform.GL.default-SG6GP0: Failed to execute child process fusermount (Permission denied)
Warning: Could not unmount revokefs-fuse filesystem at /var/tmp/flatpak-cache-CTHFP0/org.freedesktop.Platform.GL.default-SG6GP0: Failed to execute child process fusermount (Permission denied)
Installing 1/5 ................100%  1.6 MB/s  00:00Segmentation fault
[seba@seba-pc ~]$ 

------

I rebooted the system and tried to install that and other applications but the error persists. I tried installing ALT workstation-9.1 MATE x86_64 and the same thing happens.