This is ONLY if you enable margin trading via Robinhood Gold - they increased their margin requirements recently on GME and this will not happen to you if you are trading on cash.
All accounts are "Robinhood Instant" by default. You need to permanently opt-out of Robinhood Instant (or wait for deposits/trades to settle) to opt-out.
Edit: to add a link. This info is fairly well buried: https://robinhood.com/us/en/support/articles/robinhood-accou...