And that’s why it’s not God blesses you. It is not describing what has happened or is happening or does happen. It is recommending what should happen.

So, it is singular, not plural.

Nowadays, people drop the ”may” and just say “God Bless You”.

Someone above gave the right answer, similar to mine.

but what you are really asking about here is verb-subject agreement

singular form is “is” – God is great.

plural form is “are” – Greek gods are great.

“God bless you” is used as a directive phrase – you are telling someone something

“God blesses you” means something else, which is easy to understand if you expand the statement to “God blesses you with many things.”

P.S. make up your own mind about God and don’t listen to anyone else

Christians, Jews, and one more group that i don’t remember all think that there is 1 god.

and then the Romans, Greeks, Egyptians, Indians, Some of the Asians, Native Americans, Africans, and all of the other groups in the world think that there is 2 or more gods.

hope that helps!!!

Snowboarder25