What are my options for computing symbolic results for quantum circuits?
I have identified some possibilities:
SymPy (see also this), unfortunately, the software forces you to encode the matrix of each gate explicitly instead of working with circuits;
IBM Qiskit v0.25 operator framework, which claims
Qiskit operators fully support parameterization
even if it seems not completely true since the same error this older question holds and this issue is still open.