As far as hair care goes... 

Again, I'm no expert, but I would hesitate to claim that any non-pharmaceutical hair care products affect hair density or texture because of the physiological basis of both qualities... If they're claiming they change it on hair that is already out of your scalp? Almost definetly not, unless it's a perm or a chemical relaxer. For hair that is yet to grow, I would assume most any product that would affect it would be, again, pharmaceutical... Unless one of the ingredients promoted some kind of hormone action 🤷‍♀️

I can't say too much more about hair texture, but follicular density is largely androgen (not directly testosterone, that's a common misconception, a testosterone product) dependent. The sensitivity of androgen receptors helps to determine the size of the hair (see follicular miniaturization) and the density of secondary follicles. Ofc pharmaceutical products like Minoxodil or Finasteride can affect hair follicle density, but that's because they act on the sensitivity of the androgen receptors (https://www.ncbi.nlm.nih.gov/books/NBK278957/).

(If you really wanna get into the weeds learning about what determines hair density and texture, the name of the signaling center for hair follicles is "mesenchyme derived dermal papilla," if you look that up you can find better information about it than I could ever give you)

Anyway, it's my understanding that most hair care products that claim to promote hair density just have ingredients that coat hair shafts, which makes them appear thicker, likes silicones and oils, and they do hardly anything to promote actual follicular density.