Their is current compatibility issues between the Read&Write extension for Microsoft Edge and Apple M-series processors.
Because this extension relies on a third-party dictation service that is not yet optimized for this specific hardware, the following solutions will get you back up and running.
Switch to the Google Chrome extension: The Read&Write for Google Chrome extension is fully compatible with M-series processors and will provide the expected dictation experience.
Use the Read&Write desktop toolbar: Installing the desktop version of Read&Write on your Mac allows you to utilize the Screenshot Reader and Select to Speak features across all applications.