When any stylesheet is set on the application, even an empty one, QToolButton with MenuButtonPopup renders the arrow as raised even when the mouse is not over the button. There are other problems with the arrow rendering as well, but this is the easiest to replicate.

This is a regression introduced in 6.2.3 not present in 6.2.2

The following trivial PyQt6 script demos the issue. Remove the call to setStyleSheet() and the issue does not reproduce any more

from PyQt6.QtGui import *
from PyQt6.QtWidgets import *

app = QApplication([])
app.setStyleSheet(' ')

w = QMainWindow()
t = QToolBar()
a = t.addAction('test')
b = t.widgetForAction(a)
b.setPopupMode(QToolButton.ToolButtonPopupMode.MenuButtonPopup)
m = QMenu()
m.addAction('menutest')
b.setMenu(m)
w.addToolBar(t)
w.show()
app.exec()