Hi!
Welcome to Microsoft Q&A forum.
When Word is running on the external display (instead of the iPad screen), the app sometimes doesn’t register mouse-based text selection correctly. This is a bug in Word’s input handling under iPadOS’s extended-desktop environment.
Workaround that you can do.
- Use Word on the iPad screen Move the Word window back to the iPad’s display, text selection will immediately work again.
Submit a feedback as well to Microsoft.
- Inside Word › Help › Send Feedback › I don’t like something, mention “mouse text selection doesn’t work on external monitor (iPadOS 17/18)”.