Songs purchased from the iTunes Store (with the exception of music videos) have not had DRM for a very long time. I believe the files have internal tags identifying you as the purchaser, but that they should play fine on just any device you own that supports the AAC standard, whether made by Apple or not.
Songs imported from your own CDs also do not have DRM.
If you're having problems exporting non-DRMed songs for use on another computer belonging to you, it may be due to a lack of space on the destination drive, or to some hiccup when transferring large volumes of files.
Offline listening copies of Apple Music subscription songs do have DRM. You must listen to them using an Apple device or using Apple-provided software (e.g., for a Windows PC) that's tied to the same AppleID account under which you took out the Apple Music subscription.