That looks like the dust shutters on an optical output. Your optical cable usually pushes them open then snaps into (SNAP is needed) to get signal.
Re the different inputs ...
On my older Sony TV, I believe I found the optical out to only have a signal when the TV was receiving a TV signal. When my Charter box or BR was connected, whether by HDMI or component and audio, the optical had nothing to work with.
In MY case, with occasional OTA reception, I found no way to have 5.1 from 3 sources, the BR, the cable box, and the TV. I have 1 copper and one optical SPDIF in to my receiver, so MY election was a HDMI from BR to TV, copper SPDIF from BR to receiver, and optical SPDIF from TV to receiver. I don't have 5.1 from the cable box connected. I think I can use it instead of the TV as the source, but haven't tried.
I find the copyright stuff to impact me heavily; I'm moderately hearing impaired, and used to have a headphone amp connected to my old TV headphone jack, with a selector to hook it to the receiver. Optical makes that much harder.
I really wish that "all" audio output equipment had a fixed stereo out at some level, nominally 1V P-P, with traditional "RCA" connectors.