Even Fox has confirmed it.
NSC confirms Mike Waltz and staff used Gmail for government communication
https://www.foxnews.com/politics/nsc-confirms-mike-waltz-staff-used-gmail-government-communication.amp
The National Security Council (NSC) has clarified reporting about National Security Advisor Michael Waltz and his staffers using personal Gmail accounts for government communications.
A report published by the Washington Post on Tuesday claimed that one of Waltz's senior aides used Gmail "for highly technical conversations with colleagues at other government agencies involving sensitive military positions and powerful weapons systems relating to an ongoing conflict," according to the piece.
"While the NSC official used his Gmail account, his interagency colleagues used government-issued accounts, headers from the email correspondence show," the Post reported.