A barrel roll is one thing to perform in a transport category jet, it is a ~1G maneuver when performed correctly. A loop is altogether different. My good friend Bernardo Malfitano, https://www.understandingairplanes.com/Bernardo-Malfitano.ht... , when he worked as a Structural Methods & Allowables engineer at Boeing, was also an aerobatics pilot on the side and put on a fantastic brown-bag lunch presentation entitled "Can you loop a 747?" where he demonstrated how he calculated the weight, altitude, airspeed, and configuration points to theoretically loop a 747 while staying within the certified load limits, then did a stepwise simulation of the results. It would theoretically be possible, but it would be very close to the limit of the airplane's capabilities.

Found it - "Aerobatic Capabilities of “Marginally Aerobatic” Airplanes" - scroll down to "The Physics of Aerobatics" and click "Paper", toward the end there is a detailed summary of how a transport jet could just barely do a very ugly loop. https://www.understandingairplanes.com/online.html