You sadly can’t, it was a futur direction in the proposal that enabled multi closure syntax. There was some proponents but not enough. I think the door is not closed but one would need to write a proposal and an implementation to get some traction. For now I personally avoid using multiclosures and wrap the whole things into braces which is painful as I can’t double click.
I believe @xwu had a proposal, if not an implementation, but it never got picked up. It would likely take considerable energy to try and drive it through the evolution process. Personally I've accepted we'll never get the capability and this ergonomic misstep will live alongside unlabeled closure parameters as an unfortunate loss in readability in the language.
The omission of the [optional] first trailing closure was veryunpopular, to say the least. To say "there aren't enough proponents" isn't entirely true and I feel like the only way this would be considered is if other language features almost forced the first trailing closure to appear/be used.
Sorry it seems like I completely missed Xiaodi post and proposal. I genuinely thought the discussion ended after the proposal. I even tried to revive the subject in the Swift 6 things to revisit subject. My apologies.