Try playing a 5.1 audio source while you change the Digital Audio Out setting. This should allow you to change the setting to Dolby Digital or Dolby Digital Plus (if available).

I was playing the Gran Turismo movie on Netflix while trying to switch and it didn’t work. Sorry, I fat fingered the check mark. 
 

update: playing Netflix using the SmartTv app allows Dolby Digital 5.1 to play. Still no luck with the PS5 or Firestick

Based on my research, your TV is from 2014 and likely too old to pass through 5.1 audio from external media devices. You either need a new TV (ideally with eARC) or get an eARC adapter like the HDFury Arcana. The Arcana will allow the PS5 and Fire TV Stick to bypass your TV’s limitations and send the highest quality audio directly to the Arc like Dolby Atmos, Dolby Digital Plus, and Linear PCM.

Thanks GuitarSuperstar. 
 

update: I am able to get the TV to pass thru 5.1 using the optical out and the adaptor that came with the Sonos Arc. Do you think the tv has functionality to pass thru the audio via optical but not via HDMI ARC? Based on my testing this seems to be the case. May need to call Samsung.

Yes, it is very possible that the TV can only pass through 5.1 audio when the Arc is connected via optical.