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https://en.wikipedia.org/wiki/Trebuchet#History mentions traction trebuchets, where people pulling ropes causes the rotation of the arm and counterweight trebuchets, where gravity acting on a heavy object causes that rotation, with traction trebuchets being older (4th century BC)

We have a picture of a counterweight trebuchet from around 1187, though. That’s (late) 12th century.

Wikipedia also mentions various variants on counterweight trebuchets: “Sometimes counterweight trebuchets are separated into two or three different categories based on how their counterweights are attached. These being fixed, hanging, and hinged counterweights. A fixed counterweight is an intrinsic part of the swinging arm and its trajectory is circular. Hanging counterweights hang below the arm and drop vertically. Hinged counterweights are attached to the arm by a swinging joint. Some fixed counterweights also had a hinged component. The type described by al-Tarsusi was a hanging counterweight. Writing in 1280, Giles of Rome claimed that hinged counterweight trebuchets had a greater range than fixed counterweight types”

Could be that some variant was new around 1300, or new in Europe.