After the birth of Jesus, Herod ordered the 'massacre of the innocents, so Joseph fled to Egypt. But how did John the baptist got spared? ?

The massacre took place in the city of Bethlehem not in Judea which is where John the Baptist was born. So John the Baptist didn't have the problem that Jesus had

His mother took him out into the wilderness. His father, a priest, was killed for refusing to reveal where his wife and child were.

Mat 23:35 so that on you may come all the righteous blood shed on earth, from the blood of righteous Abel to the blood of Zechariah (father of John the baptist) the son of Barachiah, whom you murdered between the sanctuary and the altar.

John may not have been located in Bethlehem at the time, as the children there under the age of two years were slain.

https://www.biblegateway.com/passage/?search=luk+1...

JtB wasn't living in Bethlehem.

No one is saved through history but by forgiveness.

Actually Herod did not order anything of the kind. It did not happen. Herod has been dead for six years when Jesus is supposed to be have been born.

There is not one speck of historical evidence that any such event really happened. Chances are the author of Matthew's gospel was trying to draw parallels between Jesus and Moses as well as have an excuse to have Jesus born in Bethlehem but raised in Nazareth.