G751s do not support NVME unfortunately
This series was introduced when M2 was still in its infancy and NVMe protocol did not yet exist. Its not SATA either.
Your choices are limited to pretty much one drive.
Samsung SM951 AHCI version. There are two versions of the SM951 so make sure you get the right one.
If you already have one just look at the model number on that and change the size part of it and there you go.
They are slim pickings these days, mostly Fleabay or gouging places like servers for less
Your part number is Samsung MZHPV512HDGL
Sorry to say, thats pretty much your only option.
“Two things are infinite: the universe and human stupidity, I'm not sure about the former” ~ Albert Einstein