iTunes Backup Explorer is a graphical open-source tool that can show files in iPhone and iPad backups and extract them.
It supports both encrypted and non-encrypted backups, currently from iOS 10.2 onwards.
Most programs that support encrypted backups are either limited trials or expensive. There are apparently only very few open-source projects that target this issue and none that are also useful for the average user.
I started looking into this after I saw this brilliant answer on StackOverflow by andrewdotn to a question that has already been viewed more than 220.000 times. It explains in detail how iOS backups are structured and how they are encrypted, even providing a working code example.
So a huge thanks to him,
his sources iPhone Data Protection in Depth, iOS Hacker's Handbook, a GitHub comment, the iphone-dataprotection project and the Apple iOS Secutity Guide for iOS 11 (in the Web Archive)
and Forensic Analysis of iTunes Backups by Jack Farley