It is ok to call me dumb 
A fresh reinstall of LE solved the problem. It can now do EAC3 passthrough.... I had only tried to reinstall using old backups.
I lost all settings, addons, library etc ofc but it was still worth it.
In LE, go to:
System / Settings / System
Change: Settings level to expert
Then go to Kodi audio settings and select all compatible receiver modes
I had it on expert from the start. The options for EAC3 just weren't there.
Thank you for the tips anyway 
I did a test and installed win10 + kodi 21.1.0 + k-lite codec pack (not sure if that codec pack was needed tho) without changing anything at all with the setup and I was able to get eac3 passthrough to work without a hitch. This means there is nothing wrong with the hardware I guess.
I would very much prefer to use libreelec though since win10 feels so heavy compared to LE and due to some other small annoying things.
I was thinking about trying Kodi forum support but since it actually works with Kodi on another OS I doubt they could help me.
Again, any help or tips would be much appreciated.
No wise guru who can help me solve this problem?
Thank you for the reply.
Here is the log.
I have LE 12.0.1 (generic legacy) installed on my old Intel NUC D54250WYKH. It is connected to my AV receiver (Sony STR-DN1050).
I can't get EAC3/dolby digital plus to work through passthrough. In the Kodi audio settings I can only choose DTS and AC3 compatible receiver. If I choose a HDMI out not in use I see there are more options for EAC3, TrueHD etc.
All DD+ videos are sent to the receiver as PCM 2.0 channel audio.
If I choose 2.0 channels in Kodi and let Kodi transcode to AC3 I get 5.1 but what am I doing wrong or missing to be able to get real EAC3 passthrough?
Any help is appreciated.
Setup: NUC <HDMI> STR DN1050 <HDMI> Samsung TV
Best regards
