How do Trinitarians explain the almost exclusive use of singular pronouns to refer to God in the Bible? In thousands of instances in the Bible, pronouns used to describe God are singular. Every instance is singular except possibly 4. These possibilities all occur in the Old Testament.
For unitarians, those 4 instances are typically explained as God referring to himself and his angelic court. Two unitarian articles that put this forth are The Testimony of Singular Pronouns from OneGodWorship.com and Let Us Make Man from BiblicalUnitarian.com.
As the latter article concludes,

&quot;Understanding the “us” texts like this does not in any way damage the
massive evidence from the singular pronouns, yet it satisfactory
explains the verses in their context.&quot;

How do Trinitarians explain the heavily weighted use of singular pronouns to refer to God in the Bible, if God is 3 persons?
If I might put this in simple language, the Trinitarian position is that there is one God, and he exists in three persons.
It is entirely correct, grammatically and philosophically, to refer to God in the singular pronoun. He is One. This is true even if he consists of Father, Son and Holy Spirit.
It is worth pointing out that the English language (and any other human languages) were not designed to describe a being who is at the same time singular (one God) and also plural (three persons). Any choice of language or pronouns is going to be to some extent inaccurate.
Even if this were not the case, the singularity of the pronoun is not an indication against the Trinity. In English group nouns take the singular case: &quot;There is a committee. It reviews applications.&quot; &quot;It&quot; is a singular pronoun, and while in English it is gender-neutral, that is not the case for all languages.  Similarly: &quot;I joined the team. It plays football.&quot;. I believe Hebrew and Greek take the same approach.