@birdman518 One of the posture related issues that does cause pain in the thumb and index finger (actually all fingers) is thoracic outlet syndrome which I have. A slouching forward posture with the arms and head forward will aggravate it.

My physical therapist treats this with myofascial release to get the body back into better posture. She is an expert level certified PT in the John Barnes methods. It can be more common in patients with spine injuries because this area next to the spine can easily be injured at the same time. I do a lot of stretches on the pectoralis muscles on the front of the chest.

Here is some information about TOS.
https://mskneurology.com/how-truly-treat-thoracic-outlet-syndrome/