As @GenoMax told you, this refers to legacy BLAST versions. When you unpack the packages, they contain a data directory which contains substitution matrices and similar things. I think that is the directory they refer to in NetSurfP installation instructions.
What you are looking at is called legacy blast due to the fact that this software has not been supported for a long while (v.2.2.18 is probably from 2008). Said `data` directory likely originally contained blast database indexes. I don't recollect if old blast package used v.4 format indexes. NCBI still keeps an old version of v4 blast indexes from early 2020 available here. You will need to create those from relevant fasta files, if these don't work.
Edit: Looks like you can find functionality of NetSurfP in hh-suite (LINK) which is currently maintained. They also have a nice user guide available.