It happened with a deleted Qtractor.conf, too. I did some research and found out that QT6 uses $XDG_DATA_DIRS as the default search path for icons. On my machine it was set to /usr/share/xubuntu:/usr/share/xfce4:/usr/local/share:/usr/share:/var/lib/snapd/desktop:/usr/share
Setting it to $HOME/qtractor/themes where I have my icon set for Qtractor makes Qtractor start fast again.
EDIT: have to set it to /usr/share else CALF plugins will crash Qtractor when opening their GUI.
It happened with a deleted Qtractor.conf, too. I did some research and found out that QT6 uses $XDG_DATA_DIRS as the default search path for icons. On my machine it was set to /usr/share/xubuntu:/usr/share/xfce4:/usr/local/share:/usr/share:/var/lib/snapd/desktop:/usr/share
Setting it to $HOME/qtractor/themes where I have my icon set for Qtractor makes Qtractor start fast again.
EDIT: have to set it to /usr/share else CALF plugins will crash Qtractor when opening their GUI.