Im not sure QPropertyAnimation understands the contentsMargins directly as it 4 ints and not a QRect like
Geometry

I was thinking of

  def readPP(self):                                                                                   
        return self.ppval             

    def setPP(self,val):                                                                                
         self.ppval = val                                                                                
         self.wid2.setContentsMargins(val,val,val,val)
                                                                                                    
    pp = Property(int, readPP, setPP)     

and then we cheat and set setContentsMargins for the int property

import sys
from PySide2.QtWidgets import QMainWindow, QWidget, QHBoxLayout, QLabel, QDockWidget, QTabWidget, QApplication
from PySide2.QtCore import QMargins, QPropertyAnimation


class MainWindow(QWidget):
    def __init__(self):
        super(MainWindow, self).__init__()
        self.resize(400, 300)

        self.lab1 = QLabel("text for first widget")
        self.lab2 = QLabel("text for second widget")

        self.wid1 = QWidget()
        self.wid1.setMaximumSize(150, 150)
        self.wid1.setStyleSheet("background: orange;")
        self.wid1Layout = QHBoxLayout()
        self.wid1Layout.addWidget(self.lab1)
        self.wid1.setLayout(self.wid1Layout)

        self.wid2 = QWidget()
        self.wid2.setMaximumSize(150, 150)
        self.wid2.setStyleSheet("background: teal;")
        self.wid2Layout = QHBoxLayout()
        self.wid2Layout.addWidget(self.lab2)
        self.wid2.setLayout(self.wid2Layout)

        self.layout = QHBoxLayout()
        self.layout.addWidget(self.wid1)
        self.layout.addWidget(self.wid2)
        self.setLayout(self.layout)

        self.wid1.setContentsMargins(QMargins(8, 8, 8, 8))
        self.wid2.setContentsMargins(QMargins(8, 8, 8, 8))

        self.wid1.setProperty("contentsMargins", self.wid1.contentsMargins())

        self.decMarginAnim = QPropertyAnimation(self.wid1, b"contentsMargins")

    def decMargin(self):
        self.decMarginAnim.setDuration(200)
        self.decMarginAnim.setEndValue(QMargins(0, 0, 0, 0))
        self.decMarginAnim.start()

    def enterEvent(self, event):
        self.decMargin()


if __name__ == '__main__':
    app = QApplication(sys.argv)
    mw = MainWindow()
    mw.show()
    sys.exit(app.exec_())

Would you mind helping me out here with adding the property ?