How can I export all my Iphone's data from the backup data into a useable format?
A lot of phone apps store their data in a way that no other software can read. Your best option is often to use the app on your phone to somehow export the data - instead of working with backups.
A lot of the Files app can be accessed via iCloud Drive or copied into dropbox/etc. Photos can be exported by connecting your phone to a computer and importing it like you would a DSLR camera. Contacts can be synced with various PC contact apps, and from there exported as vcard files.
Some apps won't have good export options and it might be easier to just give up on that data.
Some apps, especially music and video players, have DRM specifically designed to enforce contract license terms that do not allow exporting. In the case of Apple music, the contract terms and DRM differ depending wether you downloaded the song as a &quot;subscriber&quot; or &quot;purchased&quot; the song.
Please try searching for existing questions/answers for each individual app with data you'd like to archive, and if you can't find anything, ask a separate question for each one.