Based on your answers, your follicles are likely being miniaturised by DHT while losing their oestrogen protection. That is a root cause, and it is one of the few that is actually addressable.
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The Fix That Works At The Root
Cold pressed Pumpkin Seed Oil and saw palmetto, working from the inside on the hormone that shrinks your follicles. Choose softgels if you want it simple, or drops if you would rather not swallow a pill.
Root Fix Starter
You already tried biotin and thickening shampoos. Here is the gap they left: biotin feeds the hair shaft but cannot stop the hormone shrinking the follicle. Shampoos work at the surface. The root issue is internal hormone signalling. Neither addressed DHT.