This step by step guide will show you how to automatically add lyrics to all of the songs in the macOS Music App.
Using the small and completely free app iFetchLyrics you can have the lyrics to all of the songs in your Music App automatically downloaded and added to each track.
iFetchLyrics version 2 requires macOS 10.15 (Catalina) or later, although there are older versions (v1.x) for pre-Catalina users.