My G7 also came with a m.2 SATA (Toshiba 250Gb) and I replaced it with a m.2 NVMe PCIe Samsung EVO 970 500Gb.
The benchmarks apps show an improvement of more than 7x for reading and writing. But, to tell you the truth, the difference under normal use situations is minimal.
Anyway, if you want to replace it, go for G7 BIOS setup and verify if m.2 PCIe is checked in System Configuration -> Drives, and UNcheck SATA RAID option in the setup.
I used Macrium Reflect to clone the original m.2 SSD to other internal (non m.2) SATA SSD, and then cloned again from this to the new m.2 NVMe. After this, I installed the Samsung NVMe driver, they allowed a slightly better performance than Windows default driver.