I harvested a PCIe Gen3 x2 NVMe 1.3 SSD from my older laptop, the problem is that its length is short. I've held it in place with some tape, it should hold.
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Amazon.com: PCIe Gen3 x2 USB 3.2/3.1 Card - PCI Express to 5-Port[Type C (2), Type A (3) ] USB 3.2 HUB Internal Expansion Card Contronller Adapter PCI Express Card Desktop PC Support Multiple INs : Electronics