… @RDunn and I had a project, implemented a C++ PID controller in Qspice and ran .bode test results. You need to have a system which is close-loop stable before you run .bode. You also need to determine where to put the perturbating source such that your .bode can work.
C++ PID Controller for Qspice (Community Project) - QSPICE - Qorvo Tech Forum
If you need more information about setting up .bode, you can refer to this post
Frequency Response Analysis (.bode) Study Guide - QSPICE - Qorvo Tech Forum