Your console must have either CFW (Custom Firmware) or PS3HEN activated. Original, unmodified official firmware (OFW) cannot install unofficial PKG files.
If you install a standard YouTube PKG, the app may demand that you sign into the PlayStation Network (PSN) before allowing you to watch videos. Logging into PSN on a modified console carries a minor risk of a console ban. Ps3 Youtube Pkg Download
This is arguably the most sought-after file when people search for this topic. Unlike the old official app which had a distinct "TV-style" interface, many modern PKG solutions utilize a wrapper around the YouTube TV website (tv.youtube.com). Your console must have either CFW (Custom Firmware)