Not Able to change jenkins_home directory

I have changed the jenkins_home path in /etc/default/jenkins and restarted the jenkins service, still It’s showing /var/lib/jenkins only
in echo $jenkins_home it’s showing nothing
jenkins user has full permission of the specific dir (new location)

Jenkins is managed by systemd, so changing that file directly doesn’t work. Check out this guide: Managing systemd services

After modifying jenkins home, when we log in again, old jobs will be removed?

unless you copy things from old to new jenkins_home it is like starting a new Jenkins for the first time. So no configuration will be there and Jenkins will start the installation wizard I guess

After copying everything from the old jenkins_home, I’m not able to login to jenkins UI, The credentials It’s saying invalid,when I changed the security as false in config.xml, I can just see people and build history.
Manage jenkins is not visible.