"I've tried using the max deformation from each node of total deformation in Modal Analysis to determine the PSD Displacement (m2/Hz) for Random Analysis."
Do not do that! The deformation in Modal analysis is arbitrary because there is no load in Modal analysis to create any deformation. Take the free course on Modal Analysis.
https://courses.ansys.com/index.php/courses/modal-analysis/
You are navigating away from the AIS Discovery experience