Tim Keller, who I respect very much, has written an extensive article on the decline of the American church. https://www.thegospelcoalition.org/article/tim-keller-decline-renewal-american-church/
It is, in fact, part of a yet larger work. Fuller article here.
I am one who does believe in the virgin birth, life, death, physical resurrection, and ascension of Jesus Christ, the transforming power of the Holy Spirit, ongoing need for our confession of our selfishness, and a trustworthy Bible. As one who has attended mainline protestant churches (born, in fact, in the 1950s) all my life, this article is like a punch in the stomach and makes me sad.
I’ve also recently attended churches that Keller, I believe, would label as conservative Protestant. They are growing. They are teaching about a biblical Jesus Christ, the trustworthiness of the Bible, and the compassion and service that Jesus taught (while trying not to succumb to modern secular thought).
I love my church and pray that there is hope.