Even if a law (or executive order, or a bureaucratic regulation) is Unconstitutional, that does not mean that any Tom, Dick or Harry Taxpayer has standing to challenge it.
The PLF understands this.
Which doesn’t change the fact that the ruling you cited isn’t a barrier to a taxpayer attempting to make a challenge here. If the courts want to rule that taxpayers don’t have standing to challenge a President just making up laws out of thin air to spend our tax dollars, then let the courts rule that. But they haven’t ruled that yet.