Be sure your FiOS audio settings are set to:

Audio Format > Surround

Dynamic Range > None

Audio Passthrough > Enable

First, thank you.

Audio Format was already Surround

DR was Light, now None

AP was already enabled.

Still not ATMOS (at least not showing in app)

I’m assuming you have a Netflix premium account which is required for Atmos audio.

Does your TV’s native Netflix app pass through Atmos audio?

Thanks, again for input.

Yes, Netflix premium account.

Just tried Netflix through TV app, TV screen says ATMOS (just like FiOS) but nothing on S2 screen.

Also tried Netflix through FireTV stick. ATMOS is not displayed on TV (and obviously not in S2) through FireTV stick.

FYI- Just put on Star Wars on Disney+ through FireTV stick and I am seeing the ATMOS logo in S2 app.

Something isn’t right. When you check for the Atmos logo on the Sonos app, are you backing out of the TV control screen and coming back to it AFTER the audio has started playing from the Atmos content?

What specific Fire TV Stick do you have?

According to this guide, Atmos audio from Netflix only works on the most recent Fire TV Stick: https://www.nakamichi-usa.com/the-ultimate-dolby-atmos-guide

I am only changing TV input (TV vs FiOS vs FireTV Stick). I left the app alone and when I switched to Disney+ (through FireTV Stick), the Atmos logo appeared in the S2 app.

Interesting. Mine is a 4k, but I got it earlier last year. Funny that Disney+ will broadcast in Atmos through  my FireTV but not Netflix. On FireTV, in description in Netflix, Atmos is not displayed (on the TV screen). It is, however, displayed (on the TV screen) through TV app and FiOS.

I have an Amazon 4K Fire stick,  bought a couple of months ago, and it definitely doesn't do Atmos on Netflix. It does do Atmos on Prime (surprise surprise), although there isn't much Atmos content there.

I read that above, although the “latest” FireTV Stick (1080 only, not 4k) allegedly now does support Atmos for Netflix. My concern is that I can’t get Atmos on Netflix through my other ways of accessing it (TV native app and FiOS channel 838). Both of those other means show Dolby Atmos broadcast, but it will not pass through my Sonos. (for reference, Netflix on FireTV does not show that it will broadcast in Atmos.)

Are you able to access 4K movies? I am just wondering if your premium Netflix account has not been set up properly (by Netflix I mean)

Edit. As it says Atmos in Netflix that doesn't seem likely though 

Yes, viewable in 4K.

So we have determined that your TV can pass through Dolby Atmos audio which is a good start. This means your TV settings are probably correct. We’ve also determined the FiOS and Fire TV Stick settings are also correct. Now we need to figure out what is going on with Netflix on your TV and FiOS.

Based on what I have read on Reddit, other people with your TV model have been able to get Dolby Atmos from the Netflix native app and the FiOS.

After you start an episode of Dark on Netflix, on the Sonos app, go to Settings > About My System and scroll down to the Sonos Arc information and tell me what it says after “Audio In:”.

Through FioS (Ch. 838)

Dolby Digital Plus 5.1

Is the firmware up to date on your TV and FiOS?

Yes. Checked almost every day (and confirmed latest via Sony website.)

How long have you had your Arc? Have you tried using a different HDMI cable for your FiOS?

Arc, set up since Christmas. Cable from FiOS, good idea. However, direct through TV native app, same result.

You could also try unplugging your TV and FiOS for about a minute. And see if that changes anything.

Appreciate the thought. Tried that in the beginning!

Make sure your Netflix apps are updated. I think you do that through the Google Play store on your TV from what I read.

What is your FiOS box model number?