What is the file system type of this usb3drive ?
An external drive should automatically :
⋅ mount into /media/$USER/drive’s_uuid_or_label
⋅ belong to $USER
⋅ show rwxr-xr-x rights.
It’s managed under the hood by
udisksctl in order for $USER to get full access to it.
Most of the time a chmod 777 is not a good idea : anyone has then full write access.
Only on a removable / nomad drive that may be necessary.
But it’s depending on file system type : fat, ntfs know nothing about rights and permissions and those are « emulated » by the corresponding Linux driver for those file systems. They will appear owned by root but with rwxrwxrwx rights.
Rights and permissions on a file can only be modified by its owner. That’s why you get the Operation not permitted with nemo-share : at that moment the file ( or folder ) was owned by root while Nemo is run by you so by later changing owner you worked around the permission problem.
But not sure it was the wisest way.
And am not sure nemo-share works as expected ( Nemo and recent Nautilus do act very differently on that matter ).
Sooo… just check with another external drive that the « automount » still works as expected.