Being a liar and an accused felon is working with Republican primary voters, but general election voter are different and more discerning. Trump is already shifting into general election mode.
Trump cannot provide any exculpatory evidence to refute or minimize the indictments he faces, so his next best option to accuse Biden of doing similar illegal activity. Trump had been getting an assist in that effort from James Comer, Jim Jordan and the other flying monkeys in and out of Congress.
Trump has a history of accusing his opponents of behavior that he himself is guilty of, the political equivalent of a “No, you are” playground retort. In a 2016 debate, when Hillary Clinton accused Trump of being a Russian puppet, Trump fired back with “You’re the puppet,” a comment he never explained.
Trump told supporters in Iowa that "[Biden and his allies] think they can do whatever they want - break any law, tell any lie, ruin any life, trash any norm, and get away with anything they want." Projection much? It's surprising that Trump, while he was projecting, didn't claim that Biden faces 91 felony charges.