I'm using Win10 & iTunes to backup my old iphone (ios16) so that I can restore it to my new iphone.
The iphone storage has used 81gb out of 239gb, and 'other' data uses 45gb out of 81gb!
The backup is still running after 8 hours and the backup folder size is now at 178gb.
Not really expecting anyone to know how to fix this, a few other people posted the same issue on the internet but there were no solutions.
So I've been manually setting up the new phone, icloud helps to get things like messages moved across, but tedious.
I'll leave the backup running to see how big it gets :)