It’s certainly non standard to not use the ARC port when connecting the Sonos Arc. By using the optical (what you seem to call Fiber) port, that negates the two way connection so that the TV itself can not send volume signals to the Arc.

So, in order to use any remote with the Arc, it has to be set to IR, so the Arc can ‘see’ the commands being sent to it. I haven’t delved into the programming on your TV, but you should be looking to change the output of the remote from what it is now, to IR (and the Apple Remote as well), and then go through the remote recognition process in the Sonos Controller for your Arc. It can be set to a single set of IR codes, if your Apple TV remote is sending different codes than your TV remote, one will fail, they have to be using the same. 
 

As a side note, optical is restricted to Dolby Digital 5.1, it can not carry the bandwidth necessary for an Atmos signal, so you’re potentially restricting the output from your TV by not using the ARC connection. Were it me, I’d use some sort of A/B switch on one of the HDMI inputs for devices, just so I could have the Arc connected via HDMI’s to the ARC port on the TV, but YMMV.  It’s a personal choice, in the grand scheme, neither is ‘wrong’. 

I'd  go with a switch too, something like this one.

https://www.amazon.com/Switcher-Splitter-Automatic-Support-HDCP1-4/dp/B09MM5QT3R/ref=sr_1_5

You folks are the BEST.  I switched the SONOS ARC from the optical port to the eArc port and problems solved.  My previous TV was a Samsung 3D plasma (13 years old) which had the SONOS ARC attached via its Optical Port.  All the devices (and their remotes) were able to control the SONOS ARC volume.

Thanks for the help.

Phil ...