Libreelec 12.0 installed and working nicely on my Pi 4. It seems quicker, smoother and more stable than 11. I followed the manual procedure:
1. Downloaded the Libreelec 12.0 file for the Pi 4 (https://releases.libreelec.tv/LibreELEC-RPi4…4-12.0.0.img.gz) and put it into /storage/.update.
2. Rebooted the Pi. Some update messages appeared on the TV and the operation completed smoothly in about 10 minutes.
Initially, Netflix would not work, with these messages appearing in /storage/.kodi/temp/kodi.log:
[script.module.inputstreamhelper] ['ldd', '/storage/.kodi/cdm/libwidevinecdm.so'] cmd failed
error <general>: AddOnLog: inputstream.adaptive: Initialize: Initialize: Failed to load library: /storage/.kodi/cdm/libwidevinecdm.so: wrong ELF class: ELFCLASS32
...seemingly evidencing, as stated in the release announcement, that Kodi is now 64 bit and cannot therefore load the 32-bit Widevine library. I moved the binary
# cd /storage/.kodi/cdm/
# mv libwidevinecdm.so libwidevinecdm.so.old
and tried the Netflix add-on again. It downloaded and installed a new (and presumably 64 bit) version of libwidevinecdm.so, after which Netflix worked fine.
Jim