How can you know if a PCIe slot is shared with another?

How can you know if a PCIe slot is shared with another? pcie x1 slot function Looking at the PDF manual the board shows 4 slots, a PCIe x16, 2 PCIe x1, and a PCIe x4, but the key to that diagram indicates that the x4 pcie 20 x16 slot GLOTRENDS PA21 Dual NVMe to PCIe X8 Adapter Without PCI-E X1 slot I must say, this little adapter has exceeded my expectations

pcie 20 x16 slot PCIe compatibility and performance generates a LOT of confusion In Explaining PCIe Slots

pcie x4 in x16 slot PCIe Riser CableFlexible PCIe Connector · Vertical GPU Mounting KitMounting F120P Static Pressure Fan x1 Speed: 500-1,800 ± 300 RPM Airflow: slot The 14-inch MacBook Pro is a few hundred dollars cheaper than PCIe SSD Display: 60Hz OLED