Backup and restore
On this device, Save to phone downloads the JSON, including the background, the type, and a custom background photo. Chrome can also pick a folder, and on Android that picker can be an SD card or a USB drive. Other browsers tell you to download the file and move it with the Files app. Share, when this phone has it, opens the sheet for Files, iCloud Drive, Mail, messages, and Nearby Share. Email downloads the file and opens your mail app so you can attach it. CSV is the same shelf in a spreadsheet. Prefer JSON when you intend to restore.
Merge adds releases the device does not have and replaces a copy only when the file is newer, matched by id, MusicBrainz id, or barcode. Replace clears this device first. A backup from Dropbox, Google Drive, OneDrive, pCloud, or WebDAV uses that same preview. The shelf reminds you after 14 days if you have releases and no recent backup.
Dropbox, Google Drive, OneDrive, and pCloud appear only after a public client id is configured. WebDAV asks for your server address and an app password, which stay on this phone. Sign-in stays in the browser. You can turn on an automatic backup that runs once when you open the app, and only when the last backup is more than 14 days old. It stays off until you ask.