[unknown] ping mirrors.redcorelinux.org/kaosx

That is not an url that ping can use anyway, test with something like ping 1.1.1.1 or at least use ping mirrors.redcorelinux.org, if that resolves fine, adjust your etc/pacman.d/mirrorlist to select another mirror if fosshost still does not give the needed core.db. Also make sure to sudo pacman -Syy to force a sync (and needed when changing mirrors).

pacman -Suu has absolute nothing to do with this thread, no idea why you need it (and if this is a case of constant switching between the build and stable repos, complete wrong thread to reply to).

I just want to revert i don't know how this happen

sudo pacman -Syy
error: could not open file /var/lib/pacman/sync/build.db: Unrecognized archive format
error: could not open file /var/lib/pacman/sync/core.db: Unrecognized archive format
error: could not open file /var/lib/pacman/sync/main.db: Unrecognized archive format
error: could not open file /var/lib/pacman/sync/apps.db: Unrecognized archive format

Yesterday internet was slow and broken, ok i understand what happen

sudo pacman -Rdd libcvt
sudo pacman -Suu

it's fixed, removing libcvt is better it can be removed xorg-server, but then should be explicitly installed then marked as dependant via pacman -Rdd xorg-server, -Sdd xorg-server, -D --asdeps xorg-server