You can do that with snapshot_density_matrix
Example:
from qiskit import QuantumCircuit
from qiskit.providers.aer import extensions # import aer snapshot instructions
from qiskit import execute
qc = QuantumCircuit(3)
qc.h(0)
for i in range(qc.num_qubits-1):
qc.cx(i, i+1)
display(qc.draw())
qc.snapshot_density_matrix('density_matrix',[0,1])# [0,1]select the qubit you want to visualize
backend = Aer.get_backend('aer_simulator')
result = execute(qc, backend).result()
# Extract density matrix snapshot from result object:
density_matrix = result.data()['snapshots']['density_matrix']['density_matrix'][0]['value']
#print(density_matrix)
plot_state_city(density_matrix, color=['midnightblue', 'midnightblue'],
title="New State City")
but snapshot_density_matrix replace by SaveDensityMatrix
in the future, so
from qiskit import QuantumCircuit, Aer,execute
from qiskit.visualization import plot_state_city
from qiskit.providers.aer.library import SaveDensityMatrix
qc = QuantumCircuit(3)
qc.h(0)
for i in range(qc.num_qubits-1):
qc.cx(i, i+1)
display(qc.draw())
qc.append(SaveDensityMatrix(2, label='density_matrix'),[0,1])
backend = Aer.get_backend('aer_simulator')
result = execute(qc, backend).result()
# Extract density matrix snapshot from result object:
density_matrix = result.data()['density_matrix']
#print(density_matrix)
plot_state_city(density_matrix, color=['midnightblue', 'midnightblue'],
title="New State City")
```