Environment

• Qiskit version: 2.1.0rc1
• Python version: 3.11
• Operating system: Macos

What is happening?

ParameterExpression.sympify is returning E TypeError: 'Symbol' object is not subscriptable

How can we reproduce the issue?

from qiskit.circuit import Parameter
from qiskit.circuit import ParameterVector

p_vec = ParameterVector("p", length=2)
theta = Parameter("theta")

expression = theta + 1
expression = expression.subs({theta: p_vec[0]})
expression.sympify()

What should happen?

Returning a symbolic expression that can then be converted to a symengine expression

Any suggestions?

No response