Essentially the opposite of this question:
What is the earliest recorded post-NT instance of a clear and unambiguous denial of the personhood of the Holy Spirit? When was it claimed for the first time that the Holy Spirit is not a Person, distinct from the Father and the Son, in the history of Christianity?
When did this belief reach widespread acceptance among Christians for the first time, if ever?
I take it here you are asking for a denial of 'personhood', not equal personhood?- Yes, that's what I mean. Denial of personhood regardless of whether equality is affirmed or denied. – Nov 19 '21 at 19:42