Why does the SC513G6M2NRE motherboard marked one PCIe slot [PCIe#4] and two MCIO port have no function while installed Intel non-R1S CPU?

Question:

Why does the SC513G6M2NRE motherboard marked one PCIe slot [PCIe#4] and two MCIO port have no function while installed Intel non-R1S CPU?

Answer:

First, The R1S variant of the Intel Xeon 6 (P-core "Granite Rapids") processors are a special, single-socket-only variant that have their Ultra Path Interconnect (UPI) links repurposed to provide significantly more PCIe lanes, while non-R1S CPUs are designed for both single- and multi-socket configurations and use UPI link for inter-socket communication. 

SC513G6M2NRE uses UPI1 for PCIe 5.0 x16 slot#4. UPI2 for two MCIO PCIe 5.0 x8 slots. (Yellow blocks). Both of these slots are only available while installed Intel R1S processors. If installed with non-R1S processors, then these slots are not functional.