NVMe is a bus interface standard for PCIe devices, which promises higher performance and lower latency than AHCI. Most M2 slots on motherboards use AHCI mode by default, but a growing number of vendors have started to include NVMe support.
As of this writing, all M2 slots on the ASrock Z270 Professional Gaming LGA1151 motherboard we tested support NVMe, as well as all M2 slots on the ASUS ROG Strix Z270-E Gaming LGA1151 motherboard we tested.
That being said, there are some caveats. First, not all PCIe devices support NVMe. Second, not all M2 slots on a motherboard are equal in terms of NVMe support.
Third, some PCIe devices may require a specialized driver in order to work with NVMe. Finally, while the performance of NVMe over AHCI is generally quite good, there may be cases where the performance is not quite as good as with AHCI mode.