It is important to make a backup of your iTunes (MacOS Mojave or older) or Apple Music (MacOS Catalina or newer) library so you don't lose any music or videos that you have stored in your library.
To start, navigate to the finder and select the "Music" folder.
If you do not see the music folder on the left menu bar, select Finder from the top menu bar (next to the Apple logo), and click preferences.
Check the box next to the music label and return to the normal Finder window.
Note that in MacOS Catalina or newer, your music is in a folder called "Music."
This is the folder you will need to copy over to your Google Drive to ensure your music and videos are safe.
MacOS Mojave or older: inside the Music folder, you will see a folder called "iTunes." This is the folder you will need to copy over to your Google Drive to ensure your music and videos are safe.
Depending on the size of the Music library, this could take some time to copy over to Google Drive. Please make sure the copy is complete before you close or shutdown your comptuer.