Humanities research is fairly common and definitely understandable.
Here are some published examples:
Data and its technologies now play a large and growing role in humanities research and teaching.
The Shape of Data in Digital Humanities
The volume explores the intra- and extra-academic engagement of humanities researchers
Mapping Frontier Research in the Humanities
Humanities research often involves an individual professor researching in a library in order to write a book.
How is humanities research conducted?
Humanist research is more typically research that is conducted by Humanists, or which aims to promote Humanism.
Rome was an early center of humanist research and, during the second half of the fifteenth century, numerous Latin comedies and tragedies were being staged...
A Cultural History of Theatre in the Early Modern Age
Humanist education research is centrally concerned with promoting equity and social justice through research relationships. Humanist research takes as its starting point the dignity and humanity of all people.
The Wiley Handbook of Ethnography of Education
It appears the humanistic research is used occasionally, though far less often than humanities research: ngram