The IRS, an instrument of Congress, decides what are official government-approved churches for tax purposes, and which are not. The Catholic Church may be official, but not perhaps some small store-front operation.
But isn't that what the US Constitution says that Congress cannot do? Establish official religions? It doesn't matter if it's one, or one thousand. Some are declared official, while some are not.
The US government is not allowed to establish official religions. Yet this is what happens for IRS tax purposes.
What the government can do instead is grant religious groups non-profit status under the tax codes. That is a different test, not based on religious beliefs. But then they must be non-profit groups. Not running businesses, and not contributing to political campaigns, nor involved with them.
Most current religious organizations would retain their current tax-exempt status under this change. Except, they would be held to perhaps a more rigid standard of operating for non-profit, and non-involvement with politics. And the government would not be in the un-Constitutional business of establishing what is a religion, and what is not.