I have intel i9 12900k cpu with integrated graphics installed on my Asus Z690 MAXIMUS HERO motherboard. I am connecting my LG Ultrafine 5k (27MD5KL-B) monitor via the included thunderbolt 3 cable to my thunderbolt port on the motherboard. Unfortunately I have two issues 1) I can only use one monitor at a time -- no dual monitor with my rtx 3090 connected monitor and 2) Whenever I do use only single monitor setup with the Ultrafine, it only gives me limited 4k resolution, not the full 5k. I think it's a problem with the motherboard because technically the Intel i9 12900k is supposed to support up to 8k 7680 x 4320 at 60 Hz.
The display runs fine at 5k 60hz when I connect it to my macbook pro, however. Some people have gotten the 5k to work with other motherboards perhaps as per my research but the examples are scant.
Is there a problem with the motherboard / is there some BIOS setting I haven't figured out for the graphics or thunderbolt?