As far as i can tell amber is lacking these security updates due to downstream changes in python-apt:
https://lists.debian.org/debian-security-announce/2020/msg00216.html
https://lists.debian.org/debian-security-announce/2020/msg00012.html
https://lists.debian.org/debian-security-announce/2020/msg00229.html
See https://master.pureos.net/synchrotron/ :
python-apt buster amber 1.8.4.1 1.8.4pureos3 Requires manual merge of downstream changes with source.