The GP63 Leopard (Intel 8th Gen) series product page
overview clearly showcases NVMe SSD support. Not ALL models in this series ship or come with an SSD preinstalled though, so that is some of the specifics that you'd have to double-check with the vendor. The model-specific specifications for the GP63 Leopard-428 states it comes with a 128GB SATA M.2 SSD included, same as the newegg product page states. The manual for this series states support for both SATA and PCIe (used by NVMe SSDs) interfaces. What is not mentioned, however, is if there is an extra M.2 slot for an additional SSD, but the GP63 Leopard 8RE/reference model's specifications page
lists 2 M.2 slots, one being a combo port that supports both SATA and NVMe while the other supports NVMe only. One of the verified purchase reviews on the newegg page also states that that specific model has a second M.2 slot that takes an NVMe SSD, on which they installed a WD Black SSD that's working just fine.
I can confidently say that that model does have support for NVMe SSDs. While all M.2 sata slots do not
support NVMe SSDs, some M.2 slots do support both SATA and NVMe while others only support NVMe. In my opinion, that model is too new (generation-wise) to not support NVMe SSDs in its M.2 slot(s).