@IlovePond not a 'product', but I swear by the Denman shower brush. It's kind of a scalp massager, but been around a lot longer, and I think better than any scalp massager I've tried. I originally tried it to help work conditioner through my long hair in the shower, which it is great for - but it has also been amaaaaazing for my scalp health! I never get dandruff now, and my hair grows really fast.
Boots - often on offer, but not at the minute. LF have it on sale 😆 https://www.boots.com/denman-shower-and-massage-brush-10121990
(BTW I've found the handle can pop out sometimes, I just put a couple of drops of superglue to prevent that)
I agree with other posters - there's a limit to what you can do to hair directly, but a healthy scalp and the right food/vitamins can make a big difference.
Watching now for specific gummy and vitamin recommendations 😁