It could be that pacnew files are only created if you modified the original file. In my case, I made changes in /etc/makepkg.conf to use more threads for compilation so I got a pacnew file and merged some of the changes manually.
If you never made any changes in /etc/makepkg.conf to begin with, the update could have just overwritten the file with all of the changes.
I also found it weird that creating a debug package is now enabled by default. The vast majority of people don’t need that and it only leads to confusion.