What actually happened was that an American television network was covering a NASCAR(stock car) race As the winner- whose name, I think, was actually Brandon- was being interviewed by one of the network's correspondents, the crowd around them started chanting "F__k Joe Biden!". To cover the sound of this- the network couldn't let swearing be transmitted, due to broadcast regulations in the States- the reporter announced, as loudly as she could, that they crowd was chanting "Let's Go, Brandon!'.

Right wingers made a big deal out of nothing over the reporter having done that, implying that her actions were a form of anti-conservative political bias, when in truth, she'd have done whatever the equivalent thing would have been if there'd been a crowd chanting "F__k Trump". The fact that everybody who has used this expression as political statement knows this doesn't matter to them.