Below is a small working code to diplay what I am trying to achieve.

import sys
import os
import sqlite3

from PyQt5.QtSql import *
from PyQt5.QtCore import *
from PyQt5.QtGui import *
from PyQt5.QtWidgets import *


# createDB()
# con_1 = sqlite3.connect("temp.db")

#  # create a table
# con_1.execute('''create table t1(
#    id INTEGER PRIMARY KEY, 'First Name' TEXT, 'Last Name' TEXT, 'Full Name' TEXT);''')

# # populate the table
# con_1.execute("insert into t1 ('First Name', 'Last Name', 'Full Name') values('Wade', 'Wilson', 'Wade Wilson');")
# con_1.execute("insert into t1 ('First Name', 'Last Name', 'Full Name') values('Norman', 'Osborn', 'Norman Osborn');")
# con_1.execute("insert into t1 ('First Name', 'Last Name', 'Full Name') values('Stephen', 'Strange', 'Stephen Strange');")
# con_1.commit()
# con_1.close()

class MultilineTextEditor(QStyledItemDelegate):

    def createEditor(self, parent, options, index):
        return QTextEdit(parent)

    def setEditorData(self, editor, index):
        editor.setText(index.data())

    def setModelData(self, editor, model, index):
        model.setData(index, editor.toPlainText()) 
    
    def paint(self, painter, option, index):
        value = index.data(Qt.DisplayRole)
        if  option.state & QStyle.State_Selected:
            text1 = index.data()
            doc = QTextDocument(text1)
            cursor = QTextCursor(doc)
            cursor.selectedTableCells()
            # cursor.selectedText()  <-- How to impliment this?
            # Trying out to simply select the first line!
            cursor.movePosition(QTextCursor.Start)
            cursor.movePosition(QTextCursor.EndOfLine, QTextCursor.KeepAnchor)
            format = QTextCharFormat()

            format.setFontWeight(QFont.Bold)
            format.setFontPointSize(20)
            weight = QFont.DemiBold
            format.setFontWeight(weight)
            cursor.mergeCharFormat(format)
            print(cursor.selectedText())
            # painter commands??        
            QStyledItemDelegate.paint(self, painter, option, index)
        else:
            QStyledItemDelegate.paint(self, painter, option, index)
            
class TableViewer(QMainWindow):
    def __init__(self):
        super().__init__()
        working_dir = os.getcwd()
        db_path = f"{working_dir}\temp.db"
        print(db_path)
        self.db = QSqlDatabase.addDatabase("QSQLITE")
        self.db.setDatabaseName(db_path)

        self.db.open()

        self.model = QSqlTableModel(self, self.db)   
        self.model.setTable('t1')
        self.model.select()

        self.tableView = QTableView(self)
        self.tableView.setModel(self.model)
        self.tableView.resizeColumnsToContents()
        layout = QVBoxLayout()
        layout.addWidget(self.tableView)
        
        widget = QWidget()
        widget.setLayout(layout)
        self.setCentralWidget(widget)

        self.tableView.setItemDelegateForColumn(2, MultilineTextEditor())
        self.show()

if __name__ == '__main__':
    app = QApplication(sys.argv)
    tv = TableViewer()
    sys.exit(app.exec_())

1. A SQL Lite Database (temp.db) is created in the commented out sections
2. This db is read and displayed as in Qtableview
3. The column containing full names is editable

How would you set the format (bold, Italics, underline), size or colour of selcted string? I would eventually bind the selection with say keyboard shorcuts (eg cntr + B for bold) or display a toolbar for user selection. Found an example here: https://forum.qt.io/topic/138318/how-do-you-bold-and-un-bold-a-selected-text-pyqt-or-pyside. But Im unable to implement it, even rudementarily in Qtableview cell.
The rich text data should be saved back to be retrieved from the DB. Unfortunately I am unable to find any good explainitions on Delgate –> paint.