So I bought myself a PI5 and experience exactly the same behaviour as seen on the Asus PN42 with Generic image. It doesn't matter if edid is created or not.
LG TV detects the Pi as PC and disables all kind of settings like the mentioned Clarity/TruMotion option which I really need for 4K HDR.
Sort of the same issue is discussed in RE: LG C3 OLED TV and Libreelect on the Pi4b - PC Mode Issue MaxMustermann / dmsaudio
In short:
1. Power on TV and Pi (sequence doesn't matter in this case);
2. Play Youtube 4k HDR (@24hz), micro stuttering al the time and options for Clarity greyed out;
3. Use LG Homescreen to change the icon for HDMI into something else like Streaming Box or Bluray Player;
4. Play the same video, perfect stream. TruMotion is set to Cinematic or even Natural.
5. Switch to set-top box (TV channels);
6. Switch back to LibreELEC on pi and we are back at #2.
The same on the Asus PN42 with Generic LE. On the borrowed Odroid N2+ with CoreELEC no issues.
Thanks for any input, have a great day.