DRM comes with a variety of restrictions. In the case of protected media bought from the iTunes Store before 2010 you have both playback and burn rights on up to five authorized computers, and those computers can transfer the media to Apple devices.
With DRM media downloaded as part of a subscription to Apple Music there are no burn rights. Playback and transfer is permitted while the subscription remains active. Transfer is only permitted to devices that can check the status of the subscription.
When you take a subscription to Apple Music this doesn't change the DRM status of the existing content in your library, although if you delete your local copies and then redownload or stream from Apple Music you are at risk of ending up with a DRM copy or losing access to particular tracks altogether. It all depends on exactly what you do. See Backup your iTunes for Windows library with SyncToy for a method to backup the entire library and monitor changes in it when you make subsequent updates to the backup set. As long as you retain backups of your original media files then if you close out a subscription to Apple Music you still retain all of your original media.
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