[Python] How to delete an outliner panel child to a PySide2 window in Maya?

I am trying to convert the Maya outliner to a QWidget. It works fine and shows up on screen as expected except the cleanup of it's outliner panel. I am tracking the panel of each instance through a unique object name and intend to delete them in the widget 's closeEvent. This is because I don't want the user's session to have multiple panels after the window/windows of anything using my custom widget is closed.

Despite everything I tried, each new panel that is created is never deleted, Maya just increments the name. I am really not sure what's the solution here?

Running this directly in script editor for my tests:

import typing as _t

from maya import cmds as _cmds
from PySide2 import QtCore as _QtCore
from PySide2 import QtWidgets as _QtWidgets


class MayaOutliner(_QtWidgets.QWidget):
def __init__(self, parent=None):
super(MayaOutliner, self).__init__(parent)
# Delete on close flag
self.setAttribute(_QtCore.Qt.WA_DeleteOnClose, True)
self._outliner_panel: _t.Optional[str] = None
self._main_layout = _QtWidgets.QVBoxLayout(self)
self._main_layout.setObjectName(f"MayaOutlinerMainLayout_{id(self)}")

self._setup_ui()

def _setup_ui(self):
self.setWindowTitle("Maya Outliner")
self.resize(300, 400)

self._outliner_panel = _cmds.outlinerPanel(parent=self._main_layout.objectName())
print(self._main_layout.objectName())
print(self._outliner_panel)

def closeEvent(self, event):
if self._outliner_panel:
_cmds.deleteUI(self._outliner_panel)

# This should have been false?
print(_cmds.outlinerPanel(self._outliner_panel, exists=True))

super(MayaOutliner, self).closeEvent(event)


window = MayaOutliner()
window.show()

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