In Psalm 110:1, 5, you have TWO distinct Persons Who are equally called YHWH
"YHWH said to My Lord, Sit at My right hand until I place Your enemies as Your footstool...YHWH at Your Right Hand"
We have the first YHWH Who is the Father. Then we have ADONI, My Lord, which is also a Name used for Almighty God in the Old Testament, here used for Jesus Christ. In verse 5, according to at least 20 Hebrew MT manuscripts by the Jews, instead of ADON, have YHWH. This makes the ADONI of verse 1, YHWH, which makes TWO Persons Who are equally called YHWH.
In Isaiah 48:16, we have YHWH as the Speaker, Who says that, He and the Holy Spirit, were sent by “Adonay YHWH”
In 2 Samuel 23:2, we have a very clear reference where The Holy Spirit is called YHWH:
“The Spirit of the LORD speaks by me (heb., דִּבֶּר־בִּי, is masculine); His word (heb. וּמִלָּתוֹ , is feminine, lit, “Her word”) is on my tongue. The God of Israel has spoken; the Rock of Israel has said to me”
We would have expected “אֶת־דְּבָרוֹ”, the masculine, “His word”, which would agree with “יהוה” (YHWH), which is masculine. However, with the use of the feminine, “וּמִלָּתוֹ”, it is clear that The Spirit is meant, so that “The Spirit of the Lord”, IS the subject, and refers to One, and not two Persons. It is "His Word”, that is, The Spirit’s, that is on the tongue of David. The following words also belong to the Spirit, Who is also called “The God of Israel”, and “the Rock of Israel”. Very clear testimony to the full Deity of the Holy Spirit.
Here we have THREE distinct Persons in the Old Testament, Who are equally Almighty God