I initially thought I would use the https://github.com/wastis/PulseEqualizerGui, but it seems LibreElec doesn't use pulseaudio by default and is missing pulseaudio-equalizer anyway.
I tried it too and it did work pretty well, but not with LE or CE but on a Armbian Linux Version for S912. Once setup was completed it was easier to handle (e.g. provides build in room measurement, instant manual equalization and no need for REW/RePhase !). However, here you got a more featured linux system running, not so "minimal" and "smart" as LE and CE are. Moreover and for me even more important, the room correction results with REW/RePhase and brutefir are superior (or can be superior, depending on your effort you put in ...)