The upgrade from glibc 27-3 to 28-1 causes some apps to crash (slack and zoom for me). Here's how I fixed it.
sudo pacman -U /var/cache/pacman/pkg/glibc-2.27-3-x86_64.pkg.tar.xz \
/var/cache/pacman/pkg/lib32-glibc-2.27-3-x86_64.pkg.tar.xz
/etc/pacman.conf
IgnorePkg = glibc lib32-glibc
This should get slack/zoom back up and running.
This way you will break your OS.