In the wwdc2022, Justin Jia spoke about a half height PHPickerViewController but did not give any example of code. As far as I know the documentation does not elaborate on that.
Half Height PHPickerViewController
You can use UISheetPresentationController.
UISheetPresentationController lets you present your view controller as a sheet. Before you present your view controller, configure the sheet presentation controller in its sheetPresentationController property with the behavior and appearance you want for your sheet.