Michael S. Heiser argues that Deuteronomy 32:17 teaches the existence of demons.
Michael Heiser, "Does Deuteronomy 32:17 Assume or Deny the Reality of Other Gods?," The Bible Translator 59, no. 3 (July 2008): 137–145
Conclusion
This article has argued that the best translation of Deut 32.17 involves rendering אֱלֹ֔הַ as a singular ("God"). Doing to results in a reading where the passage assumes the reality of the other gods as demonic spiritual entities. This rendering and its result are internally consistent with other statements in Deuteronomy where YHWH disinherits the nations to the governance of lesser gods who are qualitatively and ontologically inferior to YHWH.