Seeing that bancos means benches was interesting. In the Yucatán of Mexico (perhaps elsewhere) in the parks they have these white cement chairs in pairs. They are made in a way that when you sit in them you face the other person. They are pretty cool actually. I believe that they can be called: bancos confidentes, or bancos con los enamorados.
There's no v in this sentence though?
Here's a list of major differences: https://en.wikipedia.org/wiki/Spanish_dialects_and_varieties
Here's a video about v and b (the rest are really useful too):
Looks like they're generally interchangeable when it comes to talking about benches. There's a discussion here about the 'bank' meaning, but it generally seems like banco is used for the company or the building, and banca is used for 'banking' as a concept, a general industry like banca personal, the departments that deal with those areas in particular and so on
I think some regions might prefer banca over banco for the seat, but Duo might be focusing on a particular dialect if you like
Yeah the discussions I looked at were a bit confusing, I think the banco/banca difference for banks is a bit nuanced, so it depends what you mean by 'financial institution'! Your husband is a native speaker though, so he can probably tell you if something sounds fine or if it sounds weird in a particular sentence, that's helpful!
Don't worry too much about Duo, it's not perfect, and it does focus on a particular type of Spanish (and pronunciation etc.) as a model - it won't cover everything! And it won't necessarily show you every possibility, but if you try something like la banca where you think it's valid, and Duo says no, report it and let the owls decide