Hi Lutfij, thanks for your reply.
I didnt have any dedicated GPU prior to the RTX3090, only the integrated Intel card (Intel UHD Graphics 750).
My PSU: 750 Watt be quiet! Straight Power 11 Modular 80+ Gold (1,5 years old)
My motherboard: ASUS TUF Z590-Plus WIFI 90MB16C0-M0EAY0, BIOS AMI...