Thank you for your message. This model supports
One M.2 2230 SSD PCIe NVMe 3x2 class 35 up to 512 GB
One M.2 2280 SSD PCIe NVMe 3x4 class 40 up to 1 TB
If it is of any help of you, I 've just installed a Samsung 970 pro nvme (512GB) on my G5, after I upgraded the bios version to the latest one (version 1.10, just to be sure), and it works without changing anything on the bios. I still have to do some tests on the speeds though, but it seems fine.