Is the Kingdom of God something inside of us ?

The Kingdom of God is both within us and we are in the Kingdom of God.

Being asked by the Pharisees when the kingdom of God would come, he answered them, “The kingdom of God is not coming with signs to be observed, nor will they say, ‘Look, here it is!’ or ‘There!’ for behold, the kingdom of God is in the midst of you.” Luke 17:20-21a ESV

The term “Kingdom of God” is synonymous with the phrase, “in Christ” Blessed be the God and Father of our Lord Jesus Christ, who has blessed us “in Christ” with every spiritual blessing in the heavenly places, Ephesians 1:3 ESV

The Letters of the New Testament explain how Jesus, the “Christ”, (the Anointed One, which means, the King) lives inside of us and we in him. …but you are fellow citizens with the saints, and are of God’s household, having been built on the foundation of the apostles and prophets, Christ Jesus Himself being the corner stone, in whom the whole building, being fitted together, is growing into a holy temple in the Lord, in whom you also are being built together into a dwelling of God in the Spirit. Ephesians 2:19c-22.

Believers are the Temple of the Holy Spirit and he lives inside of us.

To them God chose to make known how great among the Gentiles are the riches of the glory of this mystery, which is Christ in you, the hope of glory. Him we proclaim, warning everyone and teaching everyone with all wisdom, that we may present everyone mature in Christ. For this I toil, struggling with all his energy that he powerfully works within me. Colossians 1:27-29 ESV