For all modern versions of macOS (including both older iTunes and newer Finder backups):
Apple doesn’t make these backup files easy to browse (they are not individual photos or contacts, but a single encrypted database), but locating the folder itself is straightforward once you know where to look. itunes iphone backup location
Officially, — Apple does not provide a built-in way to change the default backup folder. However, advanced users can use a “symbolic link” (symlink) to redirect the Backup folder to another drive (e.g., an external SSD or network drive). For all modern versions of macOS (including both