1. No older packages are inside of folder mentioned in the wiki:
ls /var/cache/pacman/pkg/ | grep linux
archlinux-appstream-data-20210423-1-any.pkg.tar.zst
archlinux-keyring-20210110-1-any.pkg.tar.zst
archlinux-wallpaper-1.6.1-1-any.pkg.tar.zst
linux-5.11.16.artix1-1-x86_64.pkg.tar.zst
linux-api-headers-5.10.13-1-any.pkg.tar.zst
linux-firmware-20210315.3568f96-1-any.pkg.tar.zst
linux-headers-5.11.16.artix1-1-x86_64.pkg.tar.zst
util-linux-2.36.2-1-x86_64.pkg.tar.zst
util-linux-libs-2.36.2-1-x86_64.pkg.tar.zst
i don't know why.
2. i looked for LTS:
sudo pacman -Ss linux-lts
system/linux-lts 5.10.32-1
The LTS Linux kernel and modules
system/linux-lts-docs 5.10.32-1
Documentation for the LTS Linux kernel
system/linux-lts-headers 5.10.32-1
Headers and scripts for building modules for the LTS Linux kernel
afterward sudo update-grub
3. The AUR-Package (aur/downgrader-git) i used in Arch to downgrade `Appstream`