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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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.