I have just tested the 512 GB M.2 NVMe SSD with Crystal Disk Mark 8.0.4. The results of the LG Gram 17 (17z90p) are 3393 MB/s read and 2975 MB/s write.There were complaints with the 2020 model in SSD performance too. Some people were buying after-market NVMe SSDs to make the system drive and using the one that came with it for slower archive storage.
Just for the sake of comparison, the 256 GB SATA SSD of my LG Gram 14 (14z980) obtained 552 MB/s (read) and 345 MB/s (write).
This is a very significant difference. I think the LG Gram 17 had some great results in the SSD test. The 8 TB SSD in the new MacBook Pros has up to 7.4 GB/s read speeds, according to Apple, but the smaller SSDs will probably be slower.