From a Jain perspective:

• There is no empirical “historical proof” that yakshas exist as real beings in the same way as verifiable ancient artifacts. Yakshas are part of Jain cosmology and devotional practice, not something proven by modern science.
• Yakshas (and Yakshinis) are described in Jain scriptures as divine guardians of Tirthankaras and sacred places. They appear in narratives, commentaries, and ritual contexts, and they are commonly depicted in temple art.
• Different Jain traditions (Digambara and Śvetāmbara) sometimes list or emphasize different Yakshas for different Tirthankaras, but the central idea is consistent: yakshas are protective, supernatural beings connected to spiritual ideals rather than historical persons.
• In terms of evidence, the strongest basis is textual and iconographic: ancient Jain texts mention yakshas, and many temples feature statues or carvings of these guardians.

If you’d like, I can summarize how Yakshas are described for specific Tirthankaras in Śvetāmbara versus Digambara sources.