任务错误：表达式类型不明确，没有类型注释

将您的代码更改为：

PhotosPicker(selection: $selectedItem, matching: .videos) {
    Image(systemName: "camera.fill")
        .resizable()
        .aspectRatio(contentMode: .fit)
        .frame(height: 20)
        .padding(2)
}
.task(id: selectedItem) {

     videoURL = nil

     do {
    
        if let data = try await selectedItem?.loadTransferable(type: Data.self) {
            
            let bytes = Double(data.count)
            let megabytes = bytes / (8 * 1024 * 1024)
            
            print("size:")
            print(megabytes)
            
            if (megabytes > 32) {
                print("too big")
            } else {

                let tempFile = TemporaryMediaFile(withData: data)
                
                let asset = tempFile.avAsset
                
                let vidWidth = await asset?.naturalSize()?.width
                let vidHeight = await asset?.naturalSize()?.height
                
                videoHeight = 160 * (vidHeight! / vidWidth!)
                videoURL = tempFile.url
            }
        } else {
            print("picking failed")
        }
    
    } catch {
        print(error)
    }
}