The map description is read when the map element is in focus, either when the element is clicked or accessed via the "tab" key and focused. Was able to hear the description when the map is in focus in Chrome, Firefox, and Edge browsers with NVDA.
After enabling a screen reader, it is recommended to launch a new browser window or refresh the page. If still encountering issues with the map description, could be related to an operating system, browser, or NVDA update.