As far as i can tell amber is lacking these security updates due to downstream changes in grub2:
https://lists.debian.org/debian-security-announce/2020/msg00141.html
(note that there was a regression update afterwards: https://lists.debian.org/debian-security-announce/2020/msg00144.html)
See https://master.pureos.net/synchrotron/
grub2 buster amber 2.02+dfsg1-20 2.02+dfsg1-4pureos1 Requires manual merge of downstream changes with source.