The country with In god we trust printed on their currency, who has "one nation, under god" as part of a pledge that children learn as part of routine schooling, who has the most senior politicians and judicial representatives polarized on religion sure as hell isn't secular in practice.
I think this is a relative concept. It's less secular than pretty much all other developed nations and also less secular than many other less developed countries
The USA is more consistently secular than any other Western country. Its constitution is essentially unchanged for 250 years and is designed to separate church and state.
In the same 250 years France had swung between extremes of religious monarchy and ultra-republicanism, back and forth. England’s monarch is also the head of its national church. Even progressive countries like Sweden and Finland have national churches with taxation rights enshrined in law and automatically collected by the state tax authorities.
These are just some examples of how many European countries retain deep state-level power to the church while the society has shifted towards secularism.
And yet no American Presidential candidate could be elected without professing faith in Christianity and Biblical literalism, because the American political system is overfitted for rural, and thus Christian, cultural influence. To the point that one of the two political parties that matter frames itself as the defenders of traditional Christian values. And thus the American Supreme Court is currently repealing decades of progressive law, removing abortion rights (based entirely on Christian principles) and making mandatory school prayer legal again.
America invokes the name of God on their money and their schoolchildren evoke "one nation under God" in their pledge of allegience. State governments constantly fight to be able to teach creationism and intelligent design in schools. Christianity is the reason you can't buy alcohol on Sundays in many places in the US. Christianity is the reason American media censors sex more so than violence. One could go on nearly ad infinitum.
Sure, there's no (officially sanctioned) national religion (It's Evangelical Christianity though) and churches don't collect taxes (rather, they don't pay taxes) but despite the secular (really, Deist) foundations of the Constitution, one would have to be blind not to see the degree to which the US is still very deeply influenced and controlled by Christianity.
Both of you are pretty much saying the same thing. The US is officially secular and has no state-sanctioned religion…The situation is that a lot (majority?) of Americans are Christians, so their ideologies and beliefs obviously affect how they vote and, consequently, many laws in the country.