Until you find out earc is a total mess as well as I believe none of the earc TV's out there do HD audio bitstreaming on earc. At least that was my understanding when I bought a C9 and at the time all I could find was that the CX would have the same issue.
By bitstreaming you mean LPCM?
I thought LG promised to send a firmware update to fix that in mid-2019...
Regardless, there's been no reason to fix anything HDMI 2.1 related considering there are no devices in the market with that output yet.
The consoles' release in November should change that. Hopefully.
I am totally clueless but can someone explain me the ARC and eARC how they work and what to they do?
ARC = Audio Return Channel. It let's the TV send the sound data to the AV Receiver through a HDMI cable.
Let's say we're using a console, a PS5.
With HDMI 2.0 we could have sound with two methods:
Normal: PS5 ---> AV Receiver-- -> TV
0000000000000000|
0000000000000000|
0000000000000 Speakers
______________________________________
ARC: PS5 ---> TV ---> AV Receiver
0000000000000000000000|
0000000000000000000000|
000000000000000000 Speakers
That way you can connect the PS5 directly to the TV to reduce latency, and still get audio from the receiver.
The problem with ARC is that it only supports either Stereo LPCM or Dolby Digital / DTS. It's the same formats as TOSLINK / optical and digital coaxial. In some cases, it supports Dolby Digital Plus which has a higher bitrate than Dolby Digital.
eARC works the same way as ARC but it adds support for Dolby TrueHD, DTS HD and up to 32 channels of uncompressed LPCM. With this, there's no quality deficit at all between using the TV or the AV Receiver as "HDMI hub", and the AV Receiver can be used for many more years / decades.