Here is my usual opening comment regarding supplements. Please remember that no matter who recommends them, they are not subjected to standardized testing nor held to any standards by the US FDA. If you choose to take them, make sure the company selling them, or the company manufacturing the capsules, subjects them to independent testing by a recognized lab. How to find out? There should be a certification seal on each bottle and a statement on their web site.

Hydrogen peroxide inhaling/nebbing is a no-go. Here is what the CDC has to say about inhaling or ingesting (Note: it is sometimes diluted and used as an oral rinse, with instructions to spit it out.)
https://wwwn.cdc.gov/TSP/MMG/MMGDetails.aspx?mmgid=304&toxid=55
Exposure can cause irritation, pneumonitis and edema. It seems unwise to introduce a potentially harmful chemical to already damaged lungs when there are no empirical studies showing the benefits.

Inhaled sulforaphane appears to have potential for improving lung function in some people with asthma, COPD and interstitial lung disease, but there is no literature about its use in Bronchiectasis, and no established dosing. All experiments to date have been very small, and I have not found information about long-term usage. It seems ingesting sulforaphane shows no similar promise.

Oxymatrine is another chemical, extracted from a specific plant in China, with possible beneficial effects for some lung conditions. Again more research is needed, and it comes with the special caveat that overdose is possible. Here it would be crucial to have certified ingredients.

If my doctor recommended either of these, I would be asking a LOT of questions about demonstrated benefits for people like me, and would want to see scientifically sound research before trying them.

Sue