[ABeeSea]

The customers that were liquidated were trading on margin (aka with borrowed money.) When you accept that borrowed money, you also agree that the broker’s risk department can liquidate your positions to ensure they get their money back.

I have not heard any anecdotes about US exchanges not allowing selling/exiting existing positions. In fact, on of the arguments from GMEanon is that disabling buying and keeping selling open drove the price down. There is nothing illegal about a broker disabling entering a new position (buying stock).