Mega-kudos to the author for chipping away at the wall around Apple’s garden. I have had a iPhone for 15 years, and I have only ever been able to back it up with iTunes on windows (as I will never buy a Mac). Apple’s refusal to provide interoperability borders on criminal. I wish there was a better option.
Have a look at https://github.com/libimobiledevice/libimobiledevice and iOS backup projects that are based on it.
[0]: https://github.com/jkcoxson/idevice