This isn't the most graceful way but still it does the job;
In the bedroom i run a small bash script with cron every night at 03:00
At 03:30 the "smart power plug" cuts power to the RPi.
Day after, the power plug scheduler starts/power on the RPi at 16:00.
(If necessary, it kan be started with remote as well...)
I do something similar, but just to reboot Kodi. Since I use another programs in background and If I not reboot Kodi will be slowly with the past of days. What I wished is do this, automatically, based on tv power on/off, and just Kodi, not LibreELEC.
But I think this is impossible.