As far as I know, dark matter hasn't made any testable predictions which were subsequently proved correct. It's an infinitely tunable hypothesis that can be retro fitted to new observations, since it has many tweakable parameters.
Could you point me to a prediction made by dark matter theory which was subsequently confirmed by observation, rather than a dark matter theory which explains it post facto?
Not sure why the downvotes just for asking a question.
Dark matter (well, LCDM) has predicted many things which were proven false, e.g. that big galaxies assembled through merging with smaller ones over long periods of time. JWST shows us this is not in fact the case. There are now lots of papers showing how LCDM can explain that, but these are post facto explanations.
Happy to be proven wrong if someone can point me to a prediction subsequently confirmed by observation.
Is this the "hot" vs "cold" dark mater discussion? (Not my area. I just read that in Wikipedia.)
Not really, Cold Dark Matter is part of LCDM, the main cosmological model. Whether hot or cold, I'd like to see a solid prediction made for it confirmed subsequently by observation.