from PySide6.QtCore import (QCoreApplication, QDate, QDateTime, QLocale,
    QMetaObject, QObject, QPoint, QRect,
    QSize, QTime, QUrl, Qt)
from PySide6.QtGui import (QBrush, QColor, QConicalGradient, QCursor,
    QFont, QFontDatabase, QGradient, QIcon,
    QImage, QKeySequence, QLinearGradient, QPainter,
    QPalette, QPixmap, QRadialGradient, QTransform)
from PySide6.QtWidgets import (QApplication, QMainWindow, QSizePolicy, QTextEdit,
    QVBoxLayout, QWidget)
class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        if not MainWindow.objectName():
            MainWindow.setObjectName(u"MainWindow")
        MainWindow.resize(363, 208)
        self.centralwidget = QWidget(MainWindow)
        self.centralwidget.setObjectName(u"centralwidget")
        self.verticalLayout = QVBoxLayout(self.centralwidget)
        self.verticalLayout.setObjectName(u"verticalLayout")
        self.textEdit = QTextEdit(self.centralwidget)
        self.textEdit.setObjectName(u"textEdit")
        font = QFont()
        font.setPointSize(14)
        self.textEdit.setFont(font)
        self.verticalLayout.addWidget(self.textEdit)
        MainWindow.setCentralWidget(self.centralwidget)
        self.retranslateUi(MainWindow)
        QMetaObject.connectSlotsByName(MainWindow)
    # setupUi
    def retranslateUi(self, MainWindow):
        MainWindow.setWindowTitle(QCoreApplication.translate("MainWindow", u"MainWindow", None))
    # retranslateUi

 from ui_untitled import *
from PySide6.QtGui import QTextBlockFormat
from sys import argv, exit
class Test(QMainWindow, Ui_MainWindow):
    def __init__(self):
        super().__init__()
        self.setupUi(self)
        self.textEdit.setText('Sample text Sample text Sample text Sample text Sample text Sample text Sample text '
                              'Sample text Sample text Sample text Sample text Sample text Sample text Sample text')
        bf = self.textEdit.textCursor().blockFormat()
        bf.setLineHeight(50, QTextBlockFormat.LineDistanceHeight)
        bf.setLineHeight(lineSpacing, QTextBlockFormat.LineDistanceHeight)
        self.textEdit.textCursor().setBlockFormat(bf)
if __name__ == "__main__":
    app = QApplication(argv)
    window = Test()
    window.show()
    exit(app.exec())

 bf.setLineHeight(lineSpacing, QTextBlockFormat.LineDistanceHeight)