It seems KDE installs it's own "octopi" icons, which make KDE's Application Launcher into thinking it should display a cardboard box instead of an octopus for the octoxbps and octoxbps-notifier applications in the "Start" menu:
[karjala@tux-void ~]$ xbps-query -f breeze-icons | grep octopi
/usr/share/icons/breeze/apps/48/octopi.svg -> /usr/share/icons/breeze/apps/48/muon.svg
/usr/share/icons/breeze-dark/apps/48/octopi.svg -> /usr/share/icons/breeze-dark/apps/48/muon.svg
Maybe one of you could change the name, eg to octoxbps-octopi?