Four Exercises to IMPROVE Your Stiff Mid-Back (Thoracic Spine Mobility).
There is less motion at the thoracic spine level, but according to [P]REHAB, the thoracic is meant to move. Thoracic extension and thoracic rotation is explained.
The Wall Angel exercise can be helpful for thoracic spinal extension.
Regarding thoracic spine rotation, you might be surprises how people minimize the function of thoracic rotation and predominantly rotate from the neck -- maybe too much rotation from the neck.