Nixos libreoffice impress slide transition sounds problem

slide transition > modify transition > sound > other sound… I select the sound file but it is not added. works fine in arch for example. works in the flatpak but that sort of defeats the object us using nixos I think. the sound file plays - it is not a codec problem. the existing sounds are in /nix/store/lnz8430mysp3rh2d0bmdzpzzvslisgsl-libreoffice-26.2.1.2/lib/libreoffice/share/gallery/sounds but I can’t add to this because it is read only. I tried putting it in /home/myname/.config/libreof...