The correct spelling of the system directory is /usr, so /usr/lib/vst would be the directory name to use.
However, you should not change the permissions on directories in /usr. If you want the plugins available for only your user you can place them into a directory within your home directory, or if you want to make the plugins available for multiple user accounts on your computer then use sudo to copy the plugin files, but leave the existing directory permissions.
only the current owner of a file/folder can change its ownership via chown.
As /usr/lib/vst is owned by root, the command has to be run by root. in your first posting/screenshot you ran “sudo …” to achieve that, it fails because the path was wrong. in the second screenshot it doesn’t work because you are not root currently, nor use sudo.
But please as ccaudle said, changing anything in /usr to be owned by your user is a bad idea.
the second hint intended to say that /usr/lib/vst is a directory, and your command would have changed only this folder’s ownership. To include all contained files, it should include the -R/–recursive option: chown -R <username> </path/to/folder>