I am also having the same problem.
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
linux-headers-amd64 : Depends: linux-headers-5.10.0-28-amd64 (= 5.10.209-2) but it is not installable
E: Unable to correct problems, you have held broken packages.
A bit out of my depth here, hoping for a fix. Any guidance would be appreciated.
EDIT: This does seem to be similar to the problem OP and I experienced in October 2023… discussion thread for that is here:
https://forums.puri.sm/t/is-linux-headers-recommended-to-be-installed/21568/8
FYI I am on a Librem Mini (original flavor)
@joao.azevedo was able to help us then, but it seems his last post on this forum was in November 2023…