Yes, HARK can perform low-pass filtering.
An example would be GHDSS (https://www.hark.jp/document/3.0.0/hark-document-en/subsec-GHDSS.html). For the GHDSS node, you can adjust the lower bound frequency and the upper bound frequency during sound separation. Depending on your need, there are also other HARK nodes that can perform such filtering (see documentation).
If my reply seems a bit off, please share more details on what you want to achieve so that I can be of better help.
HARK Support Team