I think that you are having some firewall related issues.
Try running below commands.
$sudo ufw enable
Check the status of the firewall by using the below command.
$sudo ufw status
It will show the firewall status as enable and active.
Now allow access to port 8080 by using below command.
$sudo ufw allow 8080
Now restart your Jenkins server and check the status.
$service jenkins restart
$systemctl status jenkins
You will get output like below.
jenkins status active(running)
Try accessing the 8080 port now.
I hope that it will resolve your query.