BlackRock's iShares Preferred and Income Securities ETF (PFF ETF) has allocated $380 million to preferred shares issued by Bitcoin treasury company Strategy. The perpetual preferred shares Stretch (STRC) are the fourth-largest holding in the ETF, with an allocation of $210 million. Additionally, the ETF holds other Strategy preferred shares, including $97.5 million in Strife (STRF) and $73 million in Stride (STRD), as well as $90 million in MSTR common stock.