How do Trinitarians understand what it means for Jesus to grow 'in favor' with God? Luke 2:52 says

&quot;And Jesus grew in wisdom and stature, and in favor with God and man.&quot; (Berean Study Bible)

From a unitarian perspective, the idea that Jesus, who is a man, grew in favour with God seems pretty straightforward. However, it's not clear to me how Trinitarians understand this part of the verse. Jesus is God, so how does God grow 'in favor' with God? So

Who or what exactly is being referred to by 'God' here on a standard Trinitarian interpretation?

How does Jesus, who is God, 'grow in favor' with the referent of the term 'God' - what does that mean exactly?
According to Philippians 2 we are to have within ourselves the same mind that was in Christ Jesus.  So then Jesus had, in himself, the mind that:
Though he was in the form of God He did not cling onto that but instead He emptied himself by taking the form of a servant. (v. 6-7)
Having been found in human form (servant) he humbled himself by obedience all the way to death. (v.8)
So, Jesus' mindset was that he had let go of the morphe (form) of God and took on the morphe of man.  He knew this about himself.
Obviously growth would be necessary.  He had to grow physically, mentally, etc. from a human fetus.  He had to learn language, custom, etc. as a human child.
By the time the verse in question (Luke 2:52) comes along Jesus is 12 years old.  He knows enough about who He is, at this point, (Phil 2, again) to say:

Luk 2:49  And he said to them, “Why were you looking for me? Did you not know that I must be in my Father's house?”

Literally he says &quot;the Father of me&quot;, which is the same sort of claim for which the Jews wanted to kill him later on:

Joh 5:18  This was why the Jews were seeking all the more to kill him, because not only was he breaking the Sabbath, but he was even calling God his own Father, making himself equal with God.

And he has just been in the temple for three days listening and asking questions which amazed everyone who was there:

Luk 2:46-47  After three days they found him in the temple, sitting among the teachers, listening to them and asking them questions. And all who heard him were amazed at his understanding and his answers. 

So Jesus increased in wisdom (mental) and in stature (physical) as a human being.  And also in favor (actually grace) with God and man.  He grew in grace by obedience through humility, as we all must.  This growth was part of his humility...part of the great condescension of Philippians chapter 2...part of the mystery of Godliness.
He did not grasp at the form of God which He had but He emptied Himself and took on our form.  Just as He did not abandon the form of God that He had when he came down (He did not abandon but emptied), so He did not abandon the form of a man when He went back up and lives forever as our mediator, high priest, Lord, and king.