which file can find that code?
inc/functions_search.php
oh, but it does not seem to be used, if you also change search type from fulltext to standard in the search settings.
that may be it, see if yours is set to fulltext, change to standard
It's working when set the word length to 4 and Standard search type.
but is it possible to set the word length to 2 and be a searchable?
Apache/2.4.33 (Win32) OpenSSL/1.1.0h PHP/7.2.5