Do I need 2 PCIe x16 slots to install a double slot GPU?

Go in to BIOS and Set PCIE to AUTO or Gen 4 it may be getting hung up on the gen 5 PCIE slot So boot to bios from second slot

For graphics cards, you'll always get the best results by using the fastest available PCI Express x16 slot PCI Express x8 slots can be acceptable when doing a

2in2 slot Uncompromised GPU Support Designed to Supported GPUs up to 4 slots, 343mm in length, 152mm in width ; Breathes Easy, Performs Great Breathable, mesh panels

2 long slot toaster graphics card taking up the PCIe xl 6 slot That seems to be the only method to have HDCP compliant video if you intend on building an HD-ready HTPC As for