Try to use a keyboard shortcut, hold down one or more modifier keys while pressing the last key of the shortcut. For example, to use the shortcut Command-C (copy), hold down Command, press C, then release both keys.
You can also use ctrl click. Press the ctrl key while pressing the left mouse click while dragging across the text to highlight. Then ctrl right click to highlight.
Did that work for you?
Please let me know how if you need more information.