I installed Krusader on MX Linux XFCE and i want to set Krusader to open files and folders with single click? Is it possible?

Settings -> Configure Krusader -> Panel -> Selection Mode -> Details: select "Obey global selection policy"

I tried that but it doesn't work.

You probably need to change the Mode in the left pane from Krusader Mode to Konqueror Mode. Unless your DE prevents the use of single click selection this should just work.

I changed Krusader Mode to Konqueror Mode, but single click still doesn't work. I am using MX Linux with XFCE desktop environment and Thunar file manager has single click option, which works for files and folders in Thunar, and starting shortcut on the desktop with single click, but in Krusader doesn't work.

I use Krusader 2.7.2 here on Kubuntu and that just works. So if you are using the same version you should report this as a bug: https://bugs.kde.org/enter_bug.cgi?product=krusader