Problems in powering off ubuntu 20.04

Solution 1:

You can shut down from the command line (terminal) you will need to be root to do this;

sudo -i
shutdown -h now

sudo -i - changes you to the root user, you may be asked to confirm your password.

shutdown -h now - this issues the halt command 'now' which should cause the OS to go through the shutdown process. See https://linux.die.net/man/8/shutdown

If there is a problem, you should see output on the terminal window, and in /var/log/syslog

If you are not able to shutdown in the GUI, possibly your user does not have permission, see https://unix.stackexchange.com/questions/85663/poweroff-or-reboot-as-normal-user