Files are not encrypted, but compressed. Mostly SLZ type 2 and 3 is used, so I would guess it is more similar to older titles than Anamnesis which uses mostly type 7 (zstd). Still the type 3 code for ps2 games doesn't work meaning they changed something. Judging from the type 2/3 in older games, I would say it is a LZSS variant.
This was discussed in couple of other threads before, but I don't think anyone got it working. Basically there wasn't much interest. Last I know is that chrrox dumped the decompression method from the RoF executable (it also used type 3 mostly if I remember correctly). Still I never got it to work as is. Hope someone figures this out someday