Do I need special software to get all of my music and photos off of my iPhone 6S?
For your photos, you can select them all on your Mac and then hit export using the best settings. Then you can copy them onto your Linux OS. When it comes to Apple Music, the app doesn’t run directly on Linux, as the songs have Digital Rights Management extensions (DRM).
A guide below can offer some perspective and I can offer some help with the specifics, if you need.