In some texts Copilot can not se what text you have chosen for it to work with.

The important clue is that the failure follows particular text into a clean document, while other text works. That makes another license reset or Office reinstall a poor next diagnostic step, but it does not prove the text is corrupted. Microsoft supports selecting text and invoking Copilot from the mini toolbar to edit or rewrite that selection. Test a short affected paragraph through that exact workflow, then compare it with an unaffected paragraph in the same document. Reduce the failing passage progressively until you have the smallest reproducible example. Test that sample in Word on the web as well, preserving the original document. Compare whether the selection itself is ignored or Copilot refuses the requested operation. Submit the sanitized sample, prompt, Word build, and macOS version to Microsoft Support. Until resolved, paste only the intended passage into the prompt and review the returned changes manually.