Hi Holly,
Thanks for your post in Microsoft Community.
In your description, you see a prompt in Norton that Windows Media Player needs to be updated, but you can't do it through it.
I noticed that you checked the version of Media Player, and I appreciate some of your attempts to understand the issue, and I understand the confusion of seeing an update applied in Norton but ultimately not being able to download it.
Is the “Get Windows Media Player” page you are seeing the following page?
Get Windows Media Player - Microsoft Support
If so, we can see that in Windows 10, Media Player 12 is uninstalled or available through “Optional Features”.
If you want to get a new version of Media Player, you can refer to this link to uninstall and reinstall it on your computer under Optional Features.
Meanwhile, for some Windows apps that need to be updated or not, we suggest you to refer to the prompts in Microsoft Store instead of the prompts from third-party software (e.g. Norton).
Moreover, Windows Media Player 12 is a more stable version, so if it hasn't affected your usage yet, we recommend you to ignore the update information from Norton for the time being.
Thank you for your understanding and support.
Best regards,
Zev - MSFT | Microsoft Community Support Specialist