Removing Extra Space Around QTabWidget in a QMainWindow Layout in PySide2

Question

I'm working with a PySide2 application and encountering an issue where there's unexpected extra space around my QTabWidget within a QMainWindow after moving tabs to the QMenuBar. This is in a context of a QtCore.Qt.FramelessWindowHint QMainWindow.

I've tried setting the content margins of the every widgets / layouts to 0, but it doesn't seem to remove the extra space (in green on the screenshot).

Here's how the UI is structured:

• Green: QMainWindow
• Yellow: QTabWidget
• Red: QTabBar
• Blue: QMenuBar

Here's a minimal code snippet where I move tabs to the QMenuBar:

class MyWindow(QMainWindow):
    def __init__(self, *args, **kwargs):
        super().__init__()
        
        self.tab_widget = TabWidget()
    
    def toggle_frameless(self):
        layout = QHBoxLayout()
        layout.setContentsMargins(0, 0, 0, 0)
        self.menuBar().setLayout(layout)
        self.menuBar().layout().addWidget(self.tab_widget.tab_bar)
        self.menuBar().layout().addStretch()

I suspect that the QTabWidget keep the geometry of the tabs, but I can't find a way to remove this extra space. I'm attaching a screenshot to show the issue visually with colors on backgrounds: Any insights or solutions would be greatly appreciated!

Thanks in advance !