This is a good graph of essentially what happened with Silicon Valley Bank. They had a lot of assets tied up in long-term held-to-maturity securities. On paper they looked fine- the orange line. But their market value- the blue line- was hemorrhaging amidst rising interest rates.
These weren't required to be marked to market for capital ratios, but the market value is important if you have liquidity issues. SVB was facing rising withdrawals and worried investors, so these market losses became very relevant. Most large banks don't have such imbalanced asset portfolios thankfully. And the recent Fed measures will allow banks to have a good source of short-term funding if they need it.
SVB's UK arm is going to be acquired by HSBC for a pound. HSBC says it has tangible equity or £1.4 billion, so they'll make out with a nice profit. All UK depositors will be made whole. Still no buyer for the parent company SVB, but the FDIC is going to make all depositors whole as well. No direct cost to taxpayers in either case.
Any buyer of the parent company probably will make out well too. The bank had equity by all appearances.