In the last few months I have done this on 4 iMacs and 1 MacBook Air. All worked perfectly.
2015 MacBook Air, Voila Reve nvme adapter, Hynix P31 500GB nvme ssd
2017 iMac 21.5", Voila Reve adapter, Hynix P31 1TB
2014 iMac 27", Voila Reve adapter, Crucial P3 1TB
2017 iMac 27", Sintech adapter, Samsung 970 Evo Plus 1TB
2017 iMac 27", Sintech adapter, Samsung 970 Evo Plus 1TB
Here's the Voila Reve adapter that I got from Amazon:
https://amzn.eu/d/4OzpBLV
I made sure that all the SSDs were on the latest firmware before installing them. This is easiest on a Windows PC, but it's doable on a Mac with Samsung drives.
Before you install the nvme drive, the Mac MUST have already been upgraded to High Sierra. Better to make sure it is already on Big Sur or above.
A Mac that has not already been upgraded to High Sierra or above will not see an nvme drive at all. Big Sur upgraded the firmware in the Mac to prevent the sleep issues many people experience with 3rd party drives.
It takes a bit of time to strip and reassemble an iMac to do this (1-2hrs depending on your experience), but it's a 5 minute job with MacBook Airs and Pros. Then its just the lengthy process of reinstalling MacOS and restoring data if needed.
Best of luck everybody.