See in Reader
922 B
while he was saying these things
"While Peter was saying these things"
they were afraid
These adult disciples were not afraid of clouds. This phrase indicates that some kind of unusual fear came over them with the cloud. It could be translated as "they were terrified."
A voice came out of the cloud saying
If it is unnatural to talk about a voice speaking, it could be translated as "God spoke to them from the cloud, saying."
my chosen son
This can be translated as "my son, whom I have chosen" (UDB) or "my son, the chosen one." The word "chosen" is adding information about God's Son. It is not saying that God has more than one son. (See: information about Adjectives on rc://en/ta/man/translate/figs-partsofspeech)
those days
This may refer to the days until Jesus was taken up to Heaven after the resurrection or possibly the days directly after Jesus made the statement.