See → AUR (en) - rtl8821ce-dkms-git
Remove all kernels except linux612
Then install support packages
sudo pacman -Syu linux612 dkms base-devel --needed
Clone the package and build
git clone https://aur.archlinux.org/packages/rtl8821ce-dkms-git
cd rtl8821ce-dkms-git
makepkg -iscC
Note: