Dummy display


i have 4 cards installed in a machine (centos headless), and i want to make dummy displays using nvidia cards but i cant only make one working display at a time!
is it possible to use all 4 cards to make 4 different dummy displays?

configs which i have tried:

tried to run x individually too, using this config but when i start 2nd display first one stops working…

Can anyone please help me to make this work?

Thank you.