You don't need to comment out #PATH=/opt/bin:/opt/sbin:$PATH in your /etc/profile, you need that path to use the ipkg command.
Also try ls /opt/bin/ to see if ipkg has really been installed.
How to install ipkg (or opkg) package manager on Synology DiskStation
You don't need to comment out #PATH=/opt/bin:/opt/sbin:$PATH in your /etc/profile, you need that path to use the ipkg command.
Also try ls /opt/bin/ to see if ipkg has really been installed.