Get in the habit or reading through the update Announcements, and thus preparing for any eventualities before applying the update.
Edit:
This is probably one of the best explanations I’ve ever read about what a .pacnew file is and why it has to be dealt with:
Packages include default configs to provide sane defaults. As software changes, the default config also changes. Old options get removed, new options get added, etc. But what if you change your config and the default config also changes? Arch doesn’t overwrite your configuration. It creates a .pacnew file containing the new recommended configuration and notifies you about it. It’s up to you to merge the upstream changes with your changes. If you don’t do that, your config might over time shift from sane to insane. Options were replaced by new ones, but your config still has old ones. Stuff breaks.
Also see:
https://wiki.archlinux.org/title/pacman/Pacnew_and_Pacsave
And: