When did we start saying Merry Christmas?

The first commercially produced Christmas card - 1843
The origin of the phrase Merry Christmas is unclear.
The word 'mery' has been associated with Christmas from the 1500s. The first known use was thought to be in a letter from Bishop Fisher of Rochester to Thomas Cromwell in 1534:
"And this our Lord God send you a mery Christmas, and a comfortable, to your heart’s desire."
In 2022 researchers at Worcester Cathedral claimed that their bishop Charles Booth got his seasonal greeting ( "merry this Christmas") fourteen years earlier.
I this 1520  letter from Bishop Charles Booth first known use of 'merry...Christmas?

Enter Grinch

In the 1650s, Cromwell's namesake and his puritan pals were in charge. They didn't do Christmas and did not encourage merry anything. But the greeting became widespread under the Hanoverians. Its spirit, if not the exact combination of words, is present in the carol, God Rest You Merry, Gentlemen, first published in 1775.
In the Victorian period, the invention of the Christmas card and publication of A Christmas Carol established 'Merry Christmas' as the standard greeting of the season.