PCIe lanes understanding

pcie 8x slot   Dan pcie 4 ssd in pcie 3 slot

Should work fine, it's the same as putting a 16x card in to a slot that's only wired for 8x or 4x, you don't get the full bandwidth but it will

PCI Express Riser Card x8 to x16 Left Slot Adapter for 1U Servers Key Features · 2U PCIe x16 x 8 x 8 FixedRibbon riser card · Gold finger direct inserted at Slot 2 PCI-Express 16X slot · PCIe 8X slot position · PCIe 8X

hart op slot PCIe slots are used for more than just graphics cards, though few require the bandwidth of an x16 slot Some devices do, like a quad slot The MB manual says that the x8 slot shares bandwidth with the x16 slot Meaning, if I use the x8 slot, the x16 slot will operate in x8 mode