See https://docs.voidlinux.org/xbps/index.html
xbps-install -Su # equivalent to pacman -Syu
xbps-query {packagename} # query installed packages
xbps-query -R {packagename} # query repositories

# to list removeable kernels:
vkpurge list
# to remove old kernels:
vkpurge rm all
# or
vkpurge rm <pattern>
# seem man (8) vkpurge

# To remove excess packages from /var/cache/xbps/
xbps-remove -O