I think this is an example of what you are thinking of:
[...]
( 9/14) Orphaned package notification...
cython 0.29.33-1
debugedit 5.0-5
deepin-wayland 1.0.0-1
perl-parse-yapp 1.21-5
python-hid-parser 0.0.3-1
(10/14) Checking for .pacnew and .pacsave files...
.pac* files found:
/etc/shells.pacnew
/etc/default/grub.pacnew
/etc/pamac.conf.pacnew
/etc/mkinitcpio.conf.pacnew
/etc/pacman.d/mirrorlist.pacnew
/etc/plymouth/plymouthd.conf.pacnew
/etc/retroarch.cfg.pacnew
Please check and merge
(11/14) Updating icon theme caches...
(12/14) Updating the desktop file MIME type cache...
[...]
These are not warnings, more just informational notifications. You can think of them as like a “heads-up”. Dealing with orphans and .pacnew files is generally not urgent, just something that should be eventually dealt with when you have time.
The example I was thinking of was like this (Plymouth problem after update?):
The following was displayed after the update:
warning: /etc/plymouth/plymouthd.conf installed as /etc/plymouth/plymouthd.conf.pacnew WARNING: The 'plymouth-encrypt' and 'sd-plymouth' hooks are no longer exist in the package. You should replace them with 'encrypt' and 'plymouth' hooks in your 'mkinitcpio.conf'. The 'lxdm-plymouth.service', 'lightdm-plymouth.service' and 'sddm-plymouth.service' systemd service files are no longer exist in the package. You should enable 'lxdm.service', 'lightdm.service' or 'sddm.service' instead. New optional dependencies for plymouth gtk3: x11 renderer [installed]
Those are warnings, as you can see (they literally use the word “warning”). This example was from back in March. It was a case where the .pacnew files represented changes that needed to be merged immediately. Users who overlooked this message were not able to reach the desktop after rebooting, and had to restore a snapshot to do the needed maintenance.