@yeddu People have suggested that Matthew 16:28 refers to:
1 - Jesus’ transfiguration
2 - Jesus’ resurrection and receiving of His Kingdom
3 - destruction of Jerusalem in 70 AD and the end of the old covenant
4 - the final day of judgment
In my opinion, if we look at other passages like Mark 14, it is clear that Jesus was predicting something that would happen in the lifetime of the individuals with whom he was speaking. Jesus told the priests that they would see Him coming in glory. I think options 1-3 are the most likely.
Mark 14:61-65 - Again the high priest asked him, “Are you the Messiah, the Son of the Blessed One?”
62 “I am,” said Jesus. “And you will see the Son of Man sitting at the right hand of the Mighty One and coming on the clouds of heaven.”
63 The high priest tore his clothes. “Why do we need any more witnesses?” he asked. 64 “You have heard the blasphemy. What do you think?”
They all condemned him as worthy of death. 65 Then some began to spit at him; they blindfolded him, struck him with their fists, and said, “Prophesy!” And the guards took him and beat him.
One thing you need to keep in mind is that the phrase ‘coming on the clouds’ is not necessarily literally Jesus riding on clouds. In the OT, riding on the clouds was a symbol of God coming in power to judge a nation. So, consider Isaiah 19:1:
Isaiah 19:1 - A prophecy against Egypt:
See, the Lord rides on a swift cloud
and is coming to Egypt.
The idols of Egypt tremble before him,
and the hearts of the Egyptians melt with fear.
That is why some people think that Jesus’ ‘coming on the clouds’ occurred when Jerusalem was destroyed in 70 AD as Jesus predicted by the Romans.
Keep in mind that Jesus’ Kingdom is not an earthly Kingdom - so when Jesus talks about His Kingdom coming it may not be visible.
John 18:36 - Jesus said, “My kingdom is not of this world. If it were, my servants would fight to prevent my arrest by the Jewish leaders. But now my kingdom is from another place.”