Just because I agree that sudo aptitude safe-upgrade is very well thought out framework, as kindly recommended from your side:
@Photon, I see your advice as solution to this thread already (even before @Poseidon read your above post).
Such kind of upgrading to the latest of linux-image-librem5 Kernel version requires (and is nothing new) this repeated procedure (after apt update) as such upgrade, other than to minor or major Kernel revision (But what do the other digits mean here?) is much more complex and needs to be executed on top (as one more/additional full-upgrade step) of the latest PureOS official software (from official repo) regular/daily upgrade, as some kind of “standalone” upgrade related to the new/latest officially released Kernel only.
PureOS maintainers did just great job, as usual, but this time only difference is that individual/final user needs to prepare his/her Linux installation for the apt full-upgrade before proceeding with such (new distribution related) commands:
EDIT: @Photon, please correct/edit (just once replace apt with aptitude) your first post here as you wanted to have it initially.