After re-read your suggestion, I went back to re-try nightly built latest nightly built on LE12. I gave up pretty quickly previously because boot failures. I was able to boot it up after a couple of "reboot", according to other thread.
I tested two built, similar experience. Both with HEIF add-on
LibreELEC-RPi5.aarch64-12.0-nightly-20231229-4e24516.img.gz (sha256)
LibreELEC-RPi5.aarch64-12.0-nightly-20231230-36e39ea.img.gz (sha256)
Only log entries I had was
2023-12-30 10:58:48.624 T:2638 info <general>: Loading skin file: MyPics.xml, load type: KEEP_IN_MEMORY
It was same for both 12-29 and 12-30
The HEIF images were store on USB thumb drive instead of the SD card.
I dont have offical power supply, but it's strong enough to be able to play H265 12 bit video. I figured it should be good enough?