https://edoras.sdsu.edu/~vinge/misc/singularity.html
There's a lot of speculation in there, but it's pretty carefully couched in scientific terms, and particularly in what-ifs that satisfy even the most stringent demands for conservative thinking.
The whole attempt at casting transhumanism as religion is silly. Transhumanist side says, "there's no supernatural God, but sufficiently advanced technology could approximate it" - and then people turn around and say, "you see, you say enough technology is like a god, therefore you're religious and believe in God (specifically in Christian God per mainstream religion, with all its mores)".
<facepalm>
Like X != X.
A good example of atheistic, even materialistic, religion was the official doctrine of the USSR, "marxist dialectical materialism". This had all of the hallmarks of a religion, complete with religious texts, priests, condemnation of non-believers, and so on - but caked in fully materialistic and dogmatically atheist concepts.
Still, this is not the framing that people calling transhumanism a religion use. The arguments are usually trying to show parallels between transhumanist beliefs/theories and theistic religious beliefs (almost always Christianity) - specifically to say, "look, it sounds like Christianity if you substitute AI for God and Singularity for Rapture, therefore this is just rebranded Christianity, not Science", therefore implying the transhumanists are wrong. The argument is, literally, "this pattern-matches to religion therefore must be just as wrong", and I'm saying it's a dumb argument.