Throughout the year, Trump begged to debate Biden with complete indifference to the details. However, the former president and his team became reluctant to face Kamala Harris when she became the Democratic candidate. Trump fears how he would perform against a younger, more dynamic figure like Harris, so he is backpedaling now.
It doesn't matter how hard Democrats and their media allies try to act as if Trump is dodging the September debate; that claim will never be valid. He had agreed to face Biden twice after details were negotiated between their teams, so new negotiations had to occur after Harris' nomination. If she refuses this debate, then she's the one who's afraid.
There's a 42% chance that Donald Trump will debate the Democratic nominee for president once in 2024, according to the Metaculus prediction community.