I just installed /e/os on a Fairphone 5, using the community build and manual installation steps.
I too was puzzled on how to perform the last step (chmod…) as the command left me waiting to find the device and nothing happend.
I luckily found your remark about sudo and root permissions and indeed, after first getting root access with sudo su, it was a breeze. Thanks!
@Manoj : this definitely needs to be added to the guide. For the record, I am using the latest Fedora.