In order to run several Signal desktop instances in parallel, you can pass a –user-data-dir=<path> commandline option to signal-desktop.

When Signal Desktop is installed via flatpak, do the following:

1. Copy /var/lib/flatpak/app/org.signal.Signal/current/active/files/share/applications/org.signal.Signal.desktop to ~/.local/share/applications/Signal2.desktop
2. Then edit ~/.local/share/applications/Signal2.desktop and change lines 2-3 as follows (replace <user> with your username):

   Name=Signal 2
   Exec=/usr/bin/flatpak run --branch=stable --arch=x86_64 --command=signal-desktop --file-forwarding org.signal.Signal --user-data-dir=/home/<user>/.var/app/org.signal.Signal/config/Signal2 @@u %U @@

Afterwards, you should find the second instance of Signal Desktop as „Signal 2“ in your application launcher.

Sometimes Signal asks you to verify that you're a human by solving a captcha. The link after the captcha is always opened by the default Signal client profile. You can change this temporarily by setting the Exec value of the .desktop file of the default Signal client:

In /var/lib/flatpak/app/org.signal.Signal/x86_64/stable/active/files/share/applications/org.signal.Signal.desktop:

Exec=/usr/bin/flatpak run --branch=stable --arch=x86_64 --command=signal-desktop --file-forwarding org.signal.Signal --user-data-dir=/home/<user>/.var/app/org.signal.Signal/config/Signal2 @@u %U @@

When Signal Desktop is installed via snap, do the following:

1. Copy /var/lib/snapd/desktop/applications/signal-desktop_signal-desktop.desktop to ~/.local/share/applications/Signal2.desktop
2. Then edit ~/.local/share/applications/Signal2.desktop and change lines 2-3 as follows (replace <user> with your username):

   Name=Signal 2
   Exec=env BAMF_DESKTOP_FILE_HINT=/var/lib/snapd/desktop/applications/signal-desktop_signal-desktop.desktop /snap/bin/signal-desktop --no-sandbox --user-data-dir=/home/<user>/snap/signal-desktop/current/.config/Signal2 %U

Afterwards, you should find the second instance of Signal Desktop as „Signal 2“ in your application launcher.