Scientism is commonly defined as the idea that only science, specifically the scientific method, can give us answers about how the world functions. However, modern scientism™ as it exists today has degenerated even further and has completely given up on the scientific method. In lieu of that, it simply proclaims non-sensical ad hoc conclusions based on questionable a priori assumptions about how the world is supposed to work.

Measurement of accelerating galaxies in the '30s gives rise to the Hubble constant. Scientists conclude from that, without any actual proof, that there was a Big Bang (background radiation doesn't entail a Big Bang, at best it merely implies contraction)

Chemical imbalance theory of mental illness. Not proven, a lot of counter evidence, still pushed because of pharmaceutical drugs.

Most if not all practical applications (vaccines and gene therapy) resulting from Covid research

Evolutionary biology, in its different formulations (Darwin, Spencer, Dawkins), is either profoundly trivial (aka children are similar to their parents) or introduces a great array of overly simplistic a priori assumptions such as bodies not being self-regulatory, absolute genetic determinism, disregard of adaptive behavior and epigenetics. Also, evolutionary principles break down for bacterias except the most trivial ones.