Volume control moves to what the optical sent the audio to. Very few LG remotes control everything. There are better remotes like the Logitech Harmony that consolidate remotes.
This is where it's time to try the usual setup of all HDMI sources to the receiver for audio work and then the last HDMI link from the receiver output to the HDTV's ARC and CeC port. Sometimes CeC (see google) works and pulls it all together.
1. i conect my LG smart tv to a Satellite converter on hdmi for video .
2. i connect the tv to denon reciever on optical cable for audio ) the denon has no hdmi -arc )
all works fine .
the only problem is that i can not control the volume with the LG magic remote , and i have to use rhe denon remote.
how i can configure the LG remote to control over the volume come from the reciever ?