Banks can "legally" prevent you from withdrawing your own money. And also, so can investment firms/funds in traditional finance and even with direction from the FED as well. Basically, for any centralized platform in crypto or traditional finance, not you

Especially within the past few years, banks have been increasing blocking transactions related to crypto exchanges and cryptocurrency, or limiting the amounts of these transactions. This seemed to to increase even further earlier this year with the banking collapses and something of a slight to crypto(or some kind of increase in prices). But as the economy weakens even further, banks are increasingly more reluctant to part with their money, i.e., depositor or your money. Requirements/standards for loans have increased and you are also being limited/have difficulty if you try to remove/use larger portions of cash. Banks can make up all sorts of reasons like saying your transaction was "suspicious" and "it's to keep you safe" and this is completely legal. It's basically abusing Bank Secrecy Act/Anti-Money Laundering legal provisions. And it's a catch-22 because weak banks mean they want to permit less withdrawals but weak banks also mean more people want to withdraw so customers just lose.

But it is not just banks but also, investment firms as well. We have even seen Blackstone, one of the largest global players limit as well as block withdrawals from their REIT at least 3 times in the past few months. This is a completely legal measure as well for many funds called a "frozen fund" and "hardship withdrawals" where the firm freeze fund assets so as to "prevent assets from being sold at below market value when withdrawals amounts are high". Once again, investment firms can abuse this such that when investors are fed up and just their money back to freeze the fund.

There's also just the fund and the bank simply not having the assets due to mismanagement so there's literally nothing to give back to the customer. Not the be left out, there something called Federal Reserve Regulation D where the Fed can place limitations on the amount of withdrawals you can make within a period of time.

That said, all this means is not your keys, not your funds. In TradFi or crypto.

EDIT: Direction of Fed for banks, not investment firms