ACV is recommended a lot on beauty/hair blogs and sites as a natural treatment. I didn't see anything about ACV as a treatment of dandruff caused by yeast, but I did find this article (although not very resourceful) about treating dandruff caused by bacteria.
- Dandruff and Itchy Scalp Relief
The acids and enzymes in ACV kill the “bottle bacillus”, a bacteria
that is one of the causes for many scalp and hair conditions such as
dandruff, itchy scalp, hair loss and often baldness.The bacteria clogs
hair follicles allowing dry crusts to form that itch and flake.
"Bottle Bacillius" is apparently a type of bacteria that can cause dandruff when used with certain types of hair shampoos and conditioners.
Bottle bacillus works with silica & polymer based shampoos &
conditioners to clog the hair follicles forming dry crusts & thick
film to develop on the hair & scalp. ACV breaks down the film &
crusts, dissolves excess fatty deposits that form on top of the Bottle
I did not find anything specific to ACV vs any type of vinegar. Vinegar is a disinfectant and does reduce the incidence of some bacteria, which this study on the NIH shows. This study is comparing vinegar to regular kitchen cleansers, which are obviously not suitable for skin treatments.
Vinegar eliminated <3 logs10 of S. aureus and E. coli
Relatedly, a vinegar rinse does help to improve hair texture by closing the cuticles, so hair feels smoother. This site discusses the benefits of a smoother hair cuticle.
If the dandruff is being caused by an excess build-up of products and/or a type of bacteria in combination with a build-up of products, then vinegar (which is considered a natural product by the NIH) could help reduce dandruff. There doesn't seem to be any research comparing white vinegar to ACV. And, if the dandruff is being caused by yeast, there doesn't appear to be any evidence in support of that.
FYI - FWIW: I just found something on Reddit "Skincare Addition" about white vinegar vs AC vinegar. From the archived and stickied post: "PSA: Please DO NOT use baking soda on your skin. It is NOT safe."
Edit 3: Bit of confusion over white vs apple cider vinegar. I am
specifically discussing white vinegar. Apple cider vinegar has a
higher pH (about 4.25, from everything I can read). However, it is
still possible to seriously irritate your skin with ACV (I know I
have) and I have to wonder how effective it is for exfoliation."
So, it looks like there is a difference in the pH of white vinegar vs apple cider vinegar, though I don't know of evidence for why this would make a difference in treating dandruff, aside from what I've already shared.