Other people have made excellent explanations, but I'll throw in, too.

Grand juries exist to determine whether a person should be charged with a crime. Until such point as the grand jury hands down an indictment, the mere existence of a grand jury looking into a particular case is secret. Witnesses and their testimony to a grand jury are secret.

Judge Cannon, a federal judge in Florida, presiding over the case involving the indictments of Trump, Nauta, and now De Oliviera, filed a ruling today. This ruling is in response to the government's (prosecutor's) request that a Garcia Hearing to ensure that a defendant (Waltine Nauta, in this case) understands the risks involved with having an attorney who is jointly representing other related parties, and inform the defendant that they are entitled to a different attorney who does not carry such a risk. Furthermore, the government requested that specific additional supplemental information to be provided to the court should be filed under seal to preserve the secrecy of grand jury proceedings.

Judge Cannon orders Nauta to respond to the motion for a Garcia hearing by August 17, 2023, and orders that the response "shall address the legal propriety of using an out-of-district grand jury proceeding to continue to investigate and/or to seek post-indictment hearings on matters pertinent to the instant indicted matter in this district."

Federal Judge Aileen Cannon just revealed the existence of another grand jury, which is continuing to investigate and/or seeking post-indictment hearings related to the case she is adjudicating.

Apart from being a "big fucking legal no-no" that a federal judge should damned well know better than to do, this is clearly to the benefit of the defendants in the case before her, as those defendants are now on notice that there are more investigations ongoing, and that those investigations may result in additional charges. These defendants now have more opportunity to destroy evidence, get stories straight, pressure witnesses, flee, foment insurrection, etc.

The fact that issuing this order publically is such an obvious BFLNN certainly raises the question, "Does Judge Cannon want to be removed from this case?"