Motherboard setup b450 plus ii

hi people, i´m quite new to this. Can´t make motherboard asus tuf b450 pllus ii work with 5 rtx 3090 gpus, It just recognizes 2 of them. Can´t anyone help me get it work? Surely it´s a bios setup thing
I use a lynux pendrive
cpu athlon 3000g
the mb has 2 long pci and 3 short ones, it only work with the long ones.