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There is discussion of people running PureOS off an NVMe drive, as early as April 2018 - and there is also discussion of people having problems.
There has never been an unconditional claim that PureOS will boot on any non-Purism hardware. On non-Purism hardware it is always going to be hit and miss, depending on whether your boot requires blob driver or blob firmware that is not included within PureOS.
The two people quoted above as saying that it works are both using a Librem (13) laptop.
On random other hardware, it might work, it might not work - and if it doesn’t work, it might not be as a result of the NVMe boot drive. If you can be bothered, you would have to fault isolate that.