Louisiana's new "Ten Commandments" law actually contains eleven commandments

There isn't a debate.

The 14th amendment provided for the US Constitution to be incorporated down to the state level. The intent seems to have been to bring it all in together, but the US Supreme Court eventually decided on a more piecemeal approach. As cases came through about specific sections of the Constitution, the Court would decide if the section in question applied to the states. For the Establishment Clause in question here, that happened in 1947.

So yes, the text of the Establishment Clause specifically refers to federal Congress, but the 14th amendment then steps in and says it applies to the states.

Incidentally, the 2nd amendment wasn't incorporated until 2008. If states didn't otherwise have an equivalent section to their constitution (some do, some don't), they could have put up whatever gun control measures they wanted.

Law is more complicated than quoting bits of text that you like. You actually have to consider other texts (the fourteenth amendment made the bill of rights applicable to states) and case law (Everson v. Board of education confirms that states and school districts can't support specific religious activities).

No State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any State deprive any person of life, liberty, or property, without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws.

There is debate on this like there's debate on climate change. 9/10 legal scholars agree that the 14th amendment burdened the states with the same protections of rights as the federal government. That's why you're being downvoted. This is taught in grade school.

The Establishment clause has applied to state law since 1947.