Spirometric test shows 67% of function ability (3, 5 liters of 5, 2 recommended), but ct shows normal lung structure. how is this possible?

Lung function: The test checks for lung function, the ct only sees anatomical abnormalities not functional abnormalities. I see you have cat allergy, you could also have asthma and this may explain your findings.

Different tests: Cat scan is imaging of the lungs and gives us anatomic information and if any abnormality and shadows etc, spirometery tells you how your lung is functioning and can be abnormal with normal cat scan like in bronchial asthma and COPD in smokers.

Pre and Post test: CT scanning of the chest was performed to diagnose structural abnormalities, and depending on the type of scan is also used to rule out pulmonary embolism, and to examine vascular structures. Since your FEV1 is low and should be at least 80% of predicted, I would advise a review of all values. In addition, using albuterol pre and post testing can help to define reversibility.