Thank you for sharing the link. That’s probably the white paper mentioned in the link provided by @Egregius above.
Dynamic Range Compression (DRC) – similar curves are used by camera makers for lossy RAW compression. For Nikon see https://www.photonstophotos.net/NikonInfo/NEF_Compression.htm.
In a sample HiFi DNG PL9.6 output, the Linearization Table has 1024 quantization levels. It starts with 0 2 5 7 9 11 14 16 18 20 23 and ends with 64514 64641 64769 64896 65024 65151 65279 65407 65535.
To quote the DxO WP, “We apply JPEG XL with a near-lossless quality setting”. In fact, they use JXLDistance = 0.01, minimal non-zero, as mentioned above. Normally it wouldn’t compress that good but the DRC makes the trick.