Thanks for your answer and sorry for my late feedback.
Because I had good experience with LibreELEC i switch back to an option i used in the past. I go back from NFS to SMB and this solves the problem for me. Temperatur in idle droped back to around 50°C and do not go above 65°C when the RaspberryPi is in use (Music with some spectrum gimmick and movies (mpeg).
I watch the behavior the last days and in this senses the system is stable now.
If you are interested, it would be ok for me to go back to nfs for the reason to generate a log file for you.