Based on AI search:

“…while zero-point energy has not been measured directly in a straightforward manner, its existence and effects have been by experimental observations such as the Casimir effect and the Lamb shift, affirming its role in quantum mechanics.”

Just as we acknowledge the existence of an observable universe, there similarly exists an observable vacuum of space, beyond which we may attain a more precise understanding of the vacuum's nature - an infinite, intangible expanse devoid of any remnants of quantum fluctuations.