Debian based distros, this is solution...
1) sudo apt-get install qt5ct
2) Edit /etc/X11/Xsession.d/98qtconfig...... 'export QT_QPA_PLATFORMTHEME=gtk2' to 'export QT_QPA_PLATFORMTHEME=qt5ct'.
3) Restart
4) Run in terminal: qt5ct (Qt5 Configure tool)
5) <Interface><Activate items on single-click>
ArtiX doesn't have have /etc/X11/Xsession.d/ , where to config?
I put it in /etc/environment (without export)
You can also put in in your local xinirc probably, or some .profile file.
Didn't work. Will check what shows in antiX.
Only difference, antiX says: "qt5ct: using qt5ct plugin"
amurt@rasatPC:~$ qt5ct
qt5ct: using qt5ct plugin
Configuration path: "/home/amurt/.config/qt5ct"
Found solution in Arch forum. In /etc/environment
export QT_QPA_PLATFORMTHEME=qt5ct