nix on arch, fmit

gistfile1.txt

$ # following https://wiki.archlinux.org/index.php/Nix
$ # hello works
$ nix-env -iA nixpkgs.fmit
...
building '/nix/store/l8dcfc0baypl07dmdvgl38wkxcccr7bh-user-environment.drv'...
created 15 symlinks in user environment
$ fmit
bash: fmit: command not found
$ echo $PATH
/home/sergeykish/.nix-profile/bin:/opt/google-cloud-sdk/bin:/usr/local/sbin:/usr/local/bin:/usr/bin:/usr/lib/jvm/default/bin:/usr/bin/site_perl:/usr/bin/vendor_perl:/usr/bin/core_perl:/opt/plan9/bin
$ ls .nix-profile/
 15-edo.scl   19-edo.scl                              bohlen-p_et.scl    fmit.appdata.xml   fmit.svg            meanquar.scl
 16-edo.scl   22-edo.scl                             'Carlos Beta.scl'   fmit.desktop       fmit-symbolic.svg
 17-edo.scl  'Bernhard Stopper OnlyPure tuning.scl'   fmit               fmit.png           manifest.nix
$ file .nix-profile/fmit
.nix-profile/fmit: symbolic link to /nix/store/g19psb7ny0msk7wbqdic83mgy0nr95ar-fmit-1.2.14/fmit
$ .nix-profile/fmit
Free Music Instrument Tuner (Version 1.2.6)
qt.qpa.plugin: Could not find the Qt platform plugin "xcb" in ""
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Aborted (core dumped)

Yes, unfortunately qt stuff is fairly impure. Here's a hint but not a solution:
https://nixos.wiki/wiki/Qt#This_application_failed_to_start_because_it_could_not_find_or_load_the_Qt_platform_plugin_.3F.3F.3F_in_.22.22