Jesus is sitting on the right hand of Gods throne, not on it. Jesus did not seek equality with his Father.
PSALM 110:1 The Lord said to my Lord, “Sit at My right hand, Till I make Your enemies Your footstool.” (also see Luke 20:43)
His Father had a throne designated for his son ..
LUKE 1:32 He will be great, and will be called the Son of the Highest; and the Lord God will give Him the throne of His father David. 33 And He will reign over the house of Jacob forever, and of His kingdom there will be no end.”
Although there is much debate on this, and convincing arguments could be made to support the alternative view. One being using the argument of the Trinity, that God and Jesus is ‘one’. However when considering ‘oneness’, you really need to take on board the Hebraic ‘viewpoint’ of oneness - but that’s outside of this questions parameters.
REV 3:21 To him who overcomes I will grant to sit with Me on My throne, as I also overcame and sat down with My Father on His throne.
We could argue over the translation of ‘on’ [his throne]. The Greek ‘en’, which does not mean, nor naturally translate to ‘on’ - in the sense that Jesus is ‘on’ the throne. ‘en’ could also be legitimately translated as ‘by’, or ‘with’ or ‘around’. We really need to have a foundation of the Hebraic view of Gods ‘heaven’, that he sits on the Mountain of God, and on that mountain there are numerous other entities.
The Hebraic understanding of ‘on the throne’ can also be attributed to one who, although not on the [physical] throne, nevertheless has the authority as if they were.
So the point is, we really can’t assign an authoritative interpretation to Revelation 3:21, just one verse, and then use this as an argument to consider a conflict with other verses which have a wider [multiple verses] support for their view.