I'm no computer genius, but I started with a simple Google search of the error message. I found an article from Apple Support about Logic Pro that states "Other Apple music creation apps such as MainStage and GarageBand share the same Sound Library location."
So, there's a definite connection to this error among Logic Pro, GarageBand, and MainStage. At this point, "Open Anyway" is almost surely a safe option.
Additionally:
System Settings -> General -> scroll down -> Storage Settings -> Music Creation folder
Inside the Music Creation it says "All or part of this content can be removed and reinstalled later if needed."
Since the error says "Music Creation differs from previously..." I'm going to delete what's currently inside this folder. Hopefully, it will recreate the files and stop being different than before. Or, I might just click "Open Anyway" and see if that does the trick.