In the Western world that is generally true, though there is a religious revival going on in the former USSR, and its satellite states that is still playing out.
In the Middle East it's actually the opposite, with countries becoming increasingly less secular.
In Asia it's a bit more complicated. For example, we have little idea how many Christians or Muslims there actually are in China, since the state restricts religion.
There may actually be 100 million Christians in China alone, but millions hide their religion. There are 500,000 Protestant baptisms in China every year that we know of. Which sounds like an impossibly high number until you remember that there are nearly 1.4 billion people in China.