Yeah, here a better picture of the HDMI ports on your TV:
View attachment 1627181
and yes, HDMI input 3 is the ARC enabled input on that mode. THis is unusual for an LG TV.
Anyway, you must connect the ARC enablec HDMI OUTPUT on the AV receiver to the HDMI 3 ARC enabled input on your TV is wanting to use ARC to convey audio from said TV back to your AV receiver.
You should also ensure that SimpLink on the TV is enabled and turned on as well as setting the TV's audio output to the ARC option and setting this to PASS THROUGH.
Onboard the AV receiver, go into its HDMI configurations and turn on both the HDMI Control and the ARC setting.
I'd suggest you now power both the AVR and the TV into standby and reboot them. THis will or should instigate a new HDMI handshake between the 2 devices that includes the changes you made to any of the settings.
If you still have issues with accessing the audio via ARC, consider using a different HDMI cable between them.
REMEMBER, the cable going to the TV needs to be connected to the AV receiver's HDMI
OUTPUT and not one of its inputs!