umount /run/media/myuser/New\ Volume/
umount: /run/media/myuser/New Volume: target is busy.
It seems kactivitymanagerd was using it.
[root@clown myuser]# fuser -vm /run/media/myuser/New\ Volume/
USER PID ACCESS COMMAND
myuser 612 ..c.. kactivitymanage
I tried to stop the daemon but I got the following error.
root@clown myuser]# /usr/bin/kactivitymanagerd
QStandardPaths: wrong ownership on runtime directory /run/user/1000, 1000 instead of 0
After some discussion on Freenode, I got to know that when graphical apps are run with escalated priviledges, similar error is found. I guessed I was getting the error because I was trying to stop the daemon as root user. I tried changing back to my regular user and stopping the daemon. It worked and I was able to unmount the drive after that.