How do I have the NSToolbar "floating" on top of content scrollview on macOS Tahoe?

I have this MWE right here -- it has a toolbar with a random action on it, in addition to a scroll view as the content of the window, with random labels attached inside. Since the redeisgn of the NSToolbar stuff in Tahoe, I expect the share button be able to "float" on top of the scrolled out content as shown as the first image at https://developer.apple.com/documentation/TechnologyOverviews/adopting-liquid-glass.

#import <Cocoa/Cocoa.h>

@interface AppDelegate : NSObject <NSApplicationDelegate, NSToolbarDelegate>
@property (strong) NSWindow *window;
@end

@implementation AppDelegate

- (void)applicationDidFinishLaunching:(NSNotification *)notification {
    NSRect frame = NSMakeRect(100, 100, 600, 400);
    self.window = [[NSWindow alloc] initWithContentRect:frame
                                               styleMask:(NSWindowStyleMaskTitled |
                                                          NSWindowStyleMaskClosable |
                                                          NSWindowStyleMaskResizable |
                                                          NSWindowStyleMaskMiniaturizable)
                                                 backing:NSBackingStoreBuffered
                                                   defer:NO];
    [self.window setTitle:@"Scroll View + Toolbar Demo"];
    
    NSToolbar *toolbar = [[NSToolbar alloc] initWithIdentifier:@"MainToolbar"];
    toolbar.displayMode = NSToolbarDisplayModeIconAndLabel;
    toolbar.delegate = self;
    [self.window setToolbar:toolbar];
    
    NSScrollView *scrollView = [[NSScrollView alloc] initWithFrame:self.window.contentView.bounds];
    [scrollView setAutoresizingMask:(NSViewWidthSizable | NSViewHeightSizable)];
    [scrollView setHasVerticalScroller:YES];
    [scrollView setHasHorizontalScroller:YES];
    
    NSView *documentView = [[NSView alloc] initWithFrame:NSMakeRect(0, 0, 1000, 1000)];
    
    for (int i = 0; i < 10; i++) {
        NSTextField *label = [[NSTextField alloc] initWithFrame:NSMakeRect(50, 950 - i*80, 400, 40)];
        [label setStringValue:[NSString stringWithFormat:@"Sample Label #%d", i + 1]];
        [label setBezeled:NO];
        [label setDrawsBackground:NO];
        [label setEditable:NO];
        [label setSelectable:NO];
        [documentView addSubview:label];
    }
    
    [scrollView setDocumentView:documentView];
    [self.window setContentView:scrollView];
    
    [self.window makeKeyAndOrderFront:nil];
}

- (NSArray<NSToolbarItemIdentifier> *)toolbarAllowedItemIdentifiers:(NSToolbar *)toolbar {
    return @[NSToolbarFlexibleSpaceItemIdentifier, @"ShareItem"];
}

- (NSArray<NSToolbarItemIdentifier> *)toolbarDefaultItemIdentifiers:(NSToolbar *)toolbar {
    return @[@"ShareItem"];
}

- (NSToolbarItem *)toolbar:(NSToolbar *)toolbar itemForItemIdentifier:(NSToolbarItemIdentifier)itemIdentifier willBeInsertedIntoToolbar:(BOOL)flag {
    if ([itemIdentifier isEqualToString:@"ShareItem"]) {
        NSToolbarItem *shareItem = [[NSToolbarItem alloc] initWithItemIdentifier:itemIdentifier];
        shareItem.toolTip = @"Share this content";
        shareItem.image = [NSImage imageNamed:NSImageNameShareTemplate];
        shareItem.target = self;
        shareItem.action = @selector(shareAction:);
        return shareItem;
    }
    return nil;
}

- (void)shareAction:(id)sender {
    NSLog(@"Share button clicked!");
    // Here you could present a sharing service picker
    NSSharingServicePicker *picker = [[NSSharingServicePicker alloc] initWithItems:@[@"Hello, world!"]];
    [picker showRelativeToRect:[sender view].bounds ofView:[sender view] preferredEdge:NSRectEdgeMinY];
}

@end

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        NSApplication *app = [NSApplication sharedApplication];
        AppDelegate *delegate = [[AppDelegate alloc] init];
        [app setDelegate:delegate];
        [app run];
    }
    return EXIT_SUCCESS;
}

But it doesn't and produces this image:

https://imgur.com/a/kA7MzIe

I've tried to set various settings to make the top bar transparent, but all it does is that it makes it completely opaque instead. How can I make the share button float on top of the content?

P.S. the app is a single-file app, compile it with

clang -fobjc-arc -framework Cocoa -o ScrollApp toolbar.m