Tom's Hardware: NVMe drives.

[Fielder 3,738]

All of these are 4TB

https://www.tomshardware.com/reviews/best-ssds,3891.html

Crucial P3 $189 is recommended by Toms. It's PCle 3. a.k.a. 3x4

Crucial P3 Plus $226  PCle 4. a.k.a. 4x4

Crucial T700 . PCle 5 $479 

Sabrent Rocket 4 Plus PCle 4 $349

Inland Performance Plus PCle 4 $304

Western Digital Red PCle 3 $340

Western Digital Black PCle 4 $299

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If you are going to put the old NVMe drive in an enclosure to use as an external drive, read this. The chipset in the many brands of adapters is the key. One chipset brand works well. Another brand does not.

"No, I've never had the Realtek chip adapters randomly disconnect or demonstrate other errors. I saw that plenty of times with the JMicron chip adapters though."

https://www.reddit.com/r/buildapcsales/comments/s2njbc/ssd_enclosure_sabrent_usb_32_typec_enclosure_for/?sort=confidence

https://www.tomshardware.com/best-picks/best-ssd-and-hard-drive-enclosures

SABRENT USB 3.2 10Gbps Type C Tool Free Enclosure for M.2

https://www.amazon.com/dp/B08RVC6F9Y

[Fielder 3,738]

PCLe 5 will run at PCLe 3 speeds on a PCLe 3 motherboard.

PCLe 5 will run at PCLe 4 speeds on a PCLe 4 MB

PCLe4 will run at PCL3 3 speeds on PCLe 3 MB.

[Luke 782]

It's PCIe.

Cheers