In 2024, Day 21 of Advent falls on the day of Winter Solstice. That is not always the case. The dates of Advent vary from year to year:

Unlike the Date of Christmas, the First Day of Advent Varies Year to Year – Dates of the First Day of Advent for the Next Several Years

You might think that Christmas has been celebrated the same way since the day Jesus Christ was born–thousands of years ago. But that is not the case.

The date of Christmas was set to appease the ancient pagans who celebrated their holidays around the time Christmas is currently celebrated. 

Ancient Roman Festival Saturnalia and Its Influence on Modern Christmas

The seeking of Light is the theme that unites Advent Christmas and the Winter Solstice

Winter Solstice – The Day Before the New Light Begins – Make Friends with the Darkness

What are Equinoxes and Solstices? Ways We Mark the Seasons