You are seeing the notification as you have one or more developer mode extensions in Microsoft Edge
Microsoft strongly recommends turning off developer mode in Microsoft Edge as:
Extensions not verified or certified by Microsoft can be side loaded through developer mode and hence can have serious security and privacy implications
Developer mode is meant for developers to test their extensions before submitting them to Microsoft and could be exploited by bad actors to load unsafe, unverified extensions if not used with caution.
I'm a developer; I understand the risks and I don’t want to see the notification
To protect all Microsoft Edge users from any risk of exploitation through side-loading, we do not allow dismissing the notification. If you do not wish to see this notification, Microsoft recommends using Dev or Canary channel for testing your extensions.