I thought, that you want some help to get a solution for your CEC issue.
No, 12.0.1 is not the last build, so i linked already a newer version which doesn't have the issue with 2 CEC Adapter entries. It's up to you to try it or not.
The DENON supports also CEC by itself and reports as active device, so the TV can switch to HDMI 1. After that every single device connected to the DENON can signal as "active source". The last one started, wins.
Example:
TV (HDMI 1) <- DENON (HDMI 1) <- FireTV
.... DENON (HDMI 2) <- LibreELEC (KODI)
.... DENON (HDMI 3) <- Bluray
The TV exposes: "HDMI 1", "HDMI 1 Amazon FireTV", "HDMI 1 KODI...", "HDMI 1 Bluray"
The last 3 entries equals to HDMI 1, HDMI 2 and HDMI 3 of the DENON. So it's usual that you can steering only 1 of that devices with your TV remote control at the same time. It could be that the first entry ‘HDMI 1’ of the TV only passes the remote control buttons via CEC if the device connected there has reported itself as an ‘active’ source.
To realise this, you only need a properly configured CEC adapter in LibreELEC 12.0.1+ and no other components that cause additional trouble. (such as cheaply made HDMI cables, firmware, etc.), no more and no less. 