No, but you could ask Plex to make this possible - Sonos only opens up their system to music providers. What they make of it is (mostly) their choice.

I think the area you are ‘perhaps’ referring to in the App, is possibly just where a user selects which Plex server to use (but that’s only if you have more than one server). My example screenshot attached is from ‘other sources’ in the iOS version of the App and the one greyed-out is selected, the visible folder you see is just how I can select the other (different) server. 

The second screenshot attached shows the main-screen and the available categories I can choose from to view.

I will just add I redacted some things in the earlier screenshots just for security reasons, including names of servers etc. but there’s enough to hopefully explain what the two entries in other sources shows to the end user - it’s just a way to change the Plex server for then viewing on the main screen.

That’s why I gave up using the Plex option via the Sonos app - without the folder option it’s useless to me.

Thanks for the responses.  I will take this to Plex.  I can’t fathom why they have the folder search in their own player apps, but don’t turn it on for the Sonos App.  

Did you manage to contact them? Have they responded? I fully agree that with the ability to browse by folder the whole thing is of limited use...

Most local libraries are ‘usually’ arranged by ‘Artist—>Albums—>Tracks’ ..so, personally I find the Artist folder in Plex on Sonos is just as good as a folder view in my case. I tend to just use the Artist folder view with the alphabetical index down the right-hand-side. I can find things quickly that way.

Also the new Sonos search facility is good for finding things I have stored on my Plex server - see screenshots attached.

I am very happy for you (no irony intended) and I use this sequence for Jazz and Rock collection (although even there I have some old rips called CDimage that will never be found as they have almost no metadata) but it really will not work with my vast classical collection (over 1 million track of various provenience) where number of artists runs into thousands… In other words, what I don’t understand why browsing by folders which is one of the best features of Plex can’t be replicated on Sonos...