In the Gospels, Jesus famously applied the following passage to Himself, asking the Pharisees, "If then David calls him Lord, how is he his son?" (Matthew 22:41-45):
Psalm 110:1 (LSB)
1 Yahweh says to my Lord: "Sit at My right hand Until I put Your enemies as a footstool for Your feet."
Above, Jesus is identifying with the "my Lord" (David's Lord) mentioned in the passage, who will sit at the right hand of Yahweh. In the passage, the subject at the right hand of Yahweh is clearly distinct from Yahweh, and a separate subject from Him. He is exalted by Yahweh, who tells Him to sit at His right hand, while He subdues His enemies.
This passage is applied to Jesus in various ways prolifically in the New Testament (Matthew 26:64, Mark 12:36, 14:62, Luke 20:42-43, 22:69, Acts 2:34-35, 7:55-56, Romans 8:34, Ephesians 1:20, Colossians 3:1, Hebrews 1:3, 1:13, 8:1, 10:12-13, 12:2: 1 Peter 3:22). It is one of the most important passages for defining who Jesus is, His current exalted position, and, if taken straightforwardly, His distinction from Yahweh.
While there are passages in the Old Testament which can be argued to teach that Yahweh is specifically the Father (Isaiah 63:16, 64:8, etc.), this passage is even more clear, because Jesus explicitly tells believers that He is the figure sitting at the right hand of Yahweh. One does not simply say this, and then move on, if they intend at all to communicate that they themselves are Yahweh. Instead, it communicates exactly the opposite - that they are distinct from Yahweh.
The implied Trinitarian reading - that Yahweh is sitting at the right hand of Yahweh, until Yahweh makes Yahweh's enemies a footstool for Yahweh's feet - is extraordinarily convoluted, and there is no one who would not benefit from a lengthy explanation of what exactly any of that is supposed to mean. Yet, such an explanation is not provided anywhere in the New Testament's many references, nor is it ever hinted at that a mysterious saying is being put forth. Instead, rather straightforwardly, they present that Jesus is one, and Yahweh is another, and then the authors continue as one would expect them to if they did not believe that Jesus was Yahweh, and therefore, that there was nothing particularly confusing about what they were attempting to communicate by appealing to Psalm 110:1.
This is why Psalm 110:1 is such a foundational text for a Biblical Unitarian understanding of God and Jesus Christ. Jesus is the Lord of David, and has been exalted by Yahweh to the highest position of honor. Yet, He is clearly and unambiguously distinguished from Yahweh. Jesus is the Lord - but not the Lord Yahweh - the Lord Jesus Christ, the Son of God.