It’s unavoidable. If you are living in a calorie deficit for a prolonged time, you will likely experience hair loss to some extent about 3-6 months post weight loss

This happened to me. I lost about 65lbs on WW over about a year and a half. Around when I hit goal weight (150ish) I started almost fainting at times and my hair started falling out. Went to the doctor. Thyroid was fine. It was having lived in a caloric deficit for so long (even though I was losing weight very slowly) that was doing it. Came off WW, stopped restricting. Gained it all back in less than a year. YMMV.