In ancient statues, Buddha is seen wearing a yajnopaveet. But according to the neo-Buddhists, those were created by Evil Brahmins in the wrong craftsmanship, and there is no evidence in Buddhist texts. Let see evidence of Yagnopaveet from Buddhist scriptures.
In Female Bodhisattva representation, In strotram dedicated to feminine tantric goddess Brahmani, Guari, Lakshmi, Vajrayogini, Vajravarahi, etc. Referred to as नागयज्ञोपवीताङ्गं(Pīṭhastavaḥ verse5 & सर्पयज्ञोपवीत in Suprabhātastotram means body [decorated]by yajñopaveetam of Naga.
There are many practices related to the thread are found in some sects of Buddhism but they have given different connotations eg. Sai Sin in Thailand. Pali equivalent of Upnayana is “Opanayiko” it's meaning is very different in the Pali canon, it is transformed into philosophical understanding.