Hair goes through 3 stages of growth: active, transitioning, and resting. With any dietary changes, but especially calorie restriction, fewer hairs enters the first stage and more remain in the last stage leading to hair loss . This is known as "telogen effluvium" and is not uncommon in those experiencing any major change or stressor such as weight loss due to being on a low-calorie keto diet.
Another possible cause of hair loss, or lack of active hair growth, is not eating enough protein as hair is made up mostly of protein . Try eating 0.6-1 gram of protein per kilogram of body weight. More rarely, hair loss can happen due to hormonal imbalances from conditions like hypothyroidism .
Nutrient deficiencies can also show on your locks. Try consuming vitamins and minerals like zinc, biotin, vitamin B12, iron, magnesium, and vitamin E can to get stronger and healthier hair. Certain ingredients in shampoos and conditioners can irritate your scalp and damage hair. Go for gentler, sulfate and silicone-free products.