Hi. I was actually on this site looking at covid cough remedies and saw your post. I had the same symptoms as your husband (plus headaches...even migraines...when it got really bad) for over 20 years. I went to an ENT who tested me for allergies. I was allergic to candida (yeast). The doctor asked me to try a different diet. He also said a lot of people think a candida allergy and associated diet change are a bunch of bologna, and he didn't seem rock solid on it, but told me to give it a try. Basically, the diet was no bread and very low carbs. He asked me to try it for 6 weeks to see if it did anything. He said it helps some people, but not everyone. Over 8 years later, I'm still on that diet. It was like a light switch went off. I do eat a few more carbs in moderation now (I originally didn't even eat fruit), but no bread, no pasta, no potatoes. I suggest getting him tested for allergies. I do have a similar cough now coming after contracting covid a couple weeks ago, but am hopeful it will go away.

Bronchiectasis and bronchitis have similar symptoms, including mucus in your lungs and coughing. But bronchiectasis causes permanent widening of your airways; and, bronchitis is a temporary infection that doesn’t cause lasting damage.
3 sites I use: Cleveland Clinic, John Hopkins, Mayo, NHLBI.NIH.gov. Has/is hubby using inhaler with saline solution? Must gently, and often rinse mouth out with water. See specialist in bronchiectasis & yes, adults can get cystic fibrosis. For the lung, I would start with Cleveland Clinic. It took 7 pulmonologists before correctly diagnosed. Limit dairy. Homemade Lemonade, lower sugar.