GLOTRENDS PA09-X1 M.2 NVMe to PCIe 4.0 X1 Adapter

This is a PCIe ×1 slot. You can use any M.2/PCIe ×1 adapter like the Glotrends PA09-X1, or this vertical one if you do not want to block the GPU's fans.

https://www.amazon.ca/GLOTRENDS-Adapter-Installation-Bandwidth-PA09-X1/dp/B09P3HY3P3 Speeds will be slower , but unless you're transferring large files constantly you probably won't notice. They also are on AliX for a couple dollars in a different format if your PC case doesn't happen to have the extra slot at the back some come and just hang by the x1 slot or some have small x1 risers with magnets. https://www.aliexpress.com/item/1005012365039564.html Would recommend putting your slower less used nvme on these.