I recently opened some "put spreads" at Vanguard. If you don't know what a put spread is... well, neither does Vanguard! They did not detect my positions as put spreads.
A put spread is a prediction that a stock will fall. The higher priced put is bought, and a lower priced put is sold to help reduce the cost. So you might buy a GME put with a $150 strike, and then sell a GME put with a $50 strike. So you have +1 put at $150, and -1 put at $50.
When GME drops below $50, the -1 put costs you $10... but the +1 put gains $10. Once you've paid the initial price, your risk is losing the investment. Vanguard, unfortunately, treats this put spread as two isolated purchases.
Vanguard sees -1 put on GME at $50/sh, for 100 shares, and then calculates the maximum risk of $5,000 and locks up $5,000 of cash ($50 -> $0 x 100 shares). I was really surprised when I added up the maximum loss in all the short positions, and it exactly matched the cash Vanguard had locked up in my account.
Silly me, I assumed Vanguard was as good as IBKR at detecting put spreads. At IBKR, I have several put spreads with no margin required. IBKR detects that my short position exactly matches a long position at a higher price, so there's no additional money or risk involved.
Seems like Vanguard isn't the place to set up put spreads or call spreads.