This work for me:
If you have the problem, that your system is restarting after shutdown, go to the grub.cfg in the bootloader and delete the "quiet" Parameter from "set common_args". In my case it is in line 31.
After a reboot, the system does not reboot anymore after a shutdown and you can use the PowerButton Plugin
https://xpenology.com/forum/topic/12240-installing-xpenology-on-acer-aspire-h340/?do=findComment&comment=207377