Do you also have a gas stove? I’ve lived in lots of places that have unvented blowers but none of them had gas. Would be against code in almost every city in America.
I just looked it up and section M1503.1 of the 2018 International Mechanical Code has an exception for range hoods which allows most to be used ductless. Some states, CA for example, don't allow this but the majority of states just follow the IMC code.
Where I am, it's called non-conforming and, unless there's a complaint, it doesn't become a problem until you pull a building permit AND a Building Official notices.
How much maintenance do those fans require to keep working well? I feel like the common thing is to basically not touch them, and they get pretty gross and don't seem to do much.
Edit: I got downvoted for this? I feel like I've seen a lifetime of these fans being decades old and in poor shape. I think you folks are vastly overestimating how many people clean those or replace the filter.
You need to clean the filters regularly so they don’t become a fire hazard due to oil buildup; the better ones should have some kind of reminder system and will have filters that are dishwasher safe.