Debian update to buster

# huge emoji in thunderbird titles, remove by adding a new font
apt install fonts-symbola
# save and cleanup app armor, old conf prevent from opening attachment files from thunderbird.
mv /etc/apparmor.d /etc/apparmor.d_backup
apt install --reinstall apparmor apparmor-profiles apparmor-profiles-extra
# TSC_DEADLINE errata warning, update micro code
apt install intel-microcode

Reboot (I do not find out why a systemctl restart apparmor do not work, reboot is fine)