The NVMe M.2 is irrelevant if all you're doing is gaming.
It's there for content creators because of it's high transfer speeds.
The startups, load times, and launch times would only be 1 or 2 seconds faster with NVMe M.2, and SATA 3 SSD is cheaper.
But that varies based on which SATA SSD and NVMe SSD you're comparing, with some SATA SSDs actually booting more quickly than NVMe SSDs.
That being said.... you should go with a SATA 3 SSD instead of an NVMe M.2. You'll never need NVMe M.2 for gaming.
Only reason some gaming laptops use them as boot drives is because of how small they are.
Here are some benchmarks to prove how little difference they make.