someone has replied and put it back on his twitter
It's probable there is stuff they have on William, there's probably stuff on all of them that could be bad or could be made to look bad.
How actually terrible it is I wouldn't be able to guess, stuff like the Hanbury rumours level that weren't actually published in the UK media would be bad but survivable, being an asshat to staff would be bad but survivable assuming he showed proper remorse if true. There's no saint in that family or anywhere else in the world for that matter. The same could be said for most celebrities and politicians but there are reasons the papers aren't running 24/7 exposes on all they know and it's not just because they're being sat on by PR people.
The thing to point out here is that this isn't coming from the papers "talking freely" about Harry it's all coming from his own mouth, how he took loads of drugs, how he hates everyone and everything about his family and how he hated meeting poor people, how Meghan told him she had planned out a suicide etc. That's not being leaked by the press it's HIM and most of them are playing it straight in reporting it. The media hasn't even directly reported on a lot of Prince Philip stuff that they could have and Andrew would at least still be working if he hadn't blown himself up.