I was not able to find a solution as well except for M.2 SATA SSD's (P600 is a M.2 PCIe x4 card), but although not cheap a eGPU to USB-C / Thunderbolt case (without the video card) plus PCIe to M.2 PCIe x4 card could be your only option for now (I don't know anyone who can test this except for someone from a manufacturer that makes this product).
Example: https://www.asus.com/us/Graphics-Cards-Accessory/ROG-XG-STATION-2/ ROG XG STATION 2 | Graphics Card Accessories | ASUS USA
Although it is supposed be be for video card upgrades, my guess is it should work with any PCIe card from x1 to x16 and with the right adapter also a M.2 PCIe card.
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Intel doesn't offer USB-C enclosures for the Intel® SSD 600p (or any other SSD model so far). It is important to note that we don't support this configuration.
As LFM mentioned in his reply, there are few USB-C to M.2 enclosures in the market. However, most of them support SATA based M.2 drives only. If you were to try, please make sure the enclosure supports PCIe NMVe drives as well.