First make sure you enabled the jenkins cli. In short go to JENKINS_URL/me/configure add the ssh public key and then expose the ssh server port in JENKINS_URL/configureSecurity/

If you are using the user called dev and you set a fixed port to 44556, execute this:

UPDATE_LIST=$(ssh dev@localhost -p 44556 list-plugins | grep -e ')$' | awk '{ print $1 }')
if [ ! -z "${UPDATE_LIST}" ]; then 
  echo Updating Jenkins Plugins: ${UPDATE_LIST}; 
  ssh dev@localhost -p 44556 install-plugin ${UPDATE_LIST};
  ssh dev@localhost -p 44556 safe-restart;
fi

• Debian GNU/Linux 10 (buster)
• Jenkins 2.346.3 running directly on host machine (no Docker)

• https://stackoverflow.com/questions/7709993/how-can-i-update-jenkins-plugins-from-the-terminal