I have very little information about Fisetin and the published work I've found discusses Fisetin and various cancers.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC36...

The other one does discuss various chronic diseases, but talks about pulmonary diseases in general, nothing specific.

https://pubmed.ncbi.nlm.nih.gov/27671819/

Those are just quick google searches. and there may be a whole lot more. The items I list have some clinical and scientific research to support their claims that they work. Fisetin may work just fine, and there's no reason not to try it, but there's also no data that suggests it works, or very limited data.

Mucus is a major problem for a lot of us. Jean doesn't seem to want to mention it, but I have had very good luck with Fisetin that you can buy on the internet. It is a flavonoid that comes from things like strawberries and it is noted for reducing inflammation. I have posted several articles on it in these pages, and a couple of weeks ago at least two others confirmed they also have had good luck with Fisetin. Salk Institute researchers suggested using Doctors Best brand because they "know the source is good quality". Look it up on the internet. I use 100 mg before each meal. There are not a lot of studies and trials (except what Mayo Clinic is running for Covid) so it is hard to get information on dosage. Fisetin works better for me than Mucinex, and NAC has done nothing for me for about the two years I used it after my pulmo suggested it. I have stopped taking NAC and don't notice a difference. None of this works perfectly, and I still get about one session of coughing every day to clear up what has been building up in my lungs. But at least I don't have the problem every hour like I used to. The effective half life of Fisetin has been reported to be about 3.5 to 5 hours, and that seem to me my experience, too. I will bet it is a couple of years before we get results from some of the studies and trials being run. But since there are absolutely no reports that I have read about bad side effects it seems to be worth trying it. It has been reported to be working on things like stopping some cancers, and I think that is what happened with a spot in my left lung that we were going to radiate. The spot reduced and is gone in 1.5 years of scans.

Does help some also 12 mucinex
Easy breathing

Here is a description of the Mullein plant benefits and a recipe for making a Tea drink. If you use fresh, dried leaf, be sure to decant through a fine strainer cloth before serving.
https://www.webmd.com/diet/health-benefits-mull...

Some people do take it and report good results, but there is no scientific evidence that it does anything that is clinically reportable. There are many other options: mucinex, the cough remedy suggested by CBarnes above, NAC, nebulized saline solution, Huff cough, tools like the adrobika or acapella, percussion (vests and manual) and postural drainage, among others. Talk with your doc about your diagnosis and if you don't have a pulmonologist, get one.