Look like Desktop Chipset 600 series just supports gen 3 & 4[1] and PCIe gen5 ports are only available on AlderLake Desktop[2] not Mobile[3] processors.

[1] https://ark.intel.com/content/www/us/en/ark/products/series/...

[2] https://ark.intel.com/content/www/us/en/ark/products/134598/...

[3] https://ark.intel.com/content/www/us/en/ark/products/132214/...