The veneration towards the Upanishads was visible in many European thinkers and scientists. Here is two such opinions of Arthur Schopenhauer.
“The Upanishads are the production of the highest human wisdom and I consider them almost superhuman in conception, The study of the Upanishads has been a source of great inspiration and means of comfort to my soul. From every sentences of the Upanishads deep, original and sublime thoughts arise and the whole is pervaded by a high and holy and earnest spirit. In the whole world there is no study so beneficial and so elevating as that of the Upanishads. The Upanishads have been the solace of my life and will be the solace of my death,”
“The primitive wisdom of the human race will never be pushed aside by the events of Galilee. On the contrary, Indian wisdom will flow back upon Europe and produce a thorough change in our knowing and thinking “
Reference – “Glimpses of the Scriptures of Major World Religions“, By Ashok K. Sinha