Alder Lake iGP do not support HDMI 2.1 FRL signals above 18 Gbps natively. Check Intel's official website. CPUs support only 2.0 TMDS speed of 18 Gbps.
The only way this product of Gigabyte could possibly support "8K" over HDMI port is for the motherboard to host level shifter chip, which would convert DisplayPort 1.4 signal into HDMI 2.1 FRL above 18 Gbps; something similar to what Xbox SX has on its MB.
Gigabyte's advert clearly reads "Ultra HD HDMI 2.1", which means 4K/60 8-bit RGB and not 8K anything. This product, therefore, could support 8K over DisplayPort 1.4 usb-c and mini-DP, with DSC. Be aware of dubious marketing.
Unless they disclose whether the motherboard hosts level shifter chip for above 18 Gbps signals.