Script doesn't terminate itself when expected to

[EmilyGraceSeville7cf]

Hi everyone! I have a task to write a script to create a terminal-based menu for
launching flatpak applications (referred later as launcher). launcher
should allow me to choose the application to run and then close itself when the
picked application is started.

To implement this I've done this:

• have created a gui.fish script (referred later as gui) to execute launcher
  and pass several additional options for gnome-terminal like --zoom 1.5
  (full code is available here)
• have created a launcher script to launch an actual flatpak application
  (full code is available here)

The problem is that the gui is not closed when the flatpak application is started.

To reproduce this issue I've found a minimal code to show what's going on:

gui:

#!/usr/bin/env fish

set menu_path $argv[1] # path to the launcher

gnome-terminal -- $menu_path # <-- doesn't close itself when expected to

and launcher:

#!/usr/bin/env fish

gum spin -- fish --command 'flatpak run org.mozilla.firefox &'

How to fix this issue?

Edit: partial solution is to use gum spin -- setsid flatpak run org.mozilla.firefox but it
just prevents chosen application from being closed when the terminal is terminated, it doesn't
force terminal to close itself. And from what I've noticed the terminal instance closes just
when it's not the first terminal instance.