not sure, though Vanguard is now the single largest investor in MSTR. I have a self-directed investment account that I use for my son's UTMA fund. Vanguard instituted the self-managed accounts in 2023 or 2024. Can't remember.
Discussion
I did some research and found that Vanguard does offer a few mutual funds that are heavy MSTR like The Vanguard Extended Market Index Funds (VEMPX, VEMX, VEXAX).