You can’t really compare the two wrt IoT. For Debian you need an additional OTA update mechanism. Luckily rauc is in the Debian repos but you still need to setup everything yourself: A/B partitioning etc.

Mender is a nice solution for the A/B partition updates as well.

https://mender.io/

I'm surprised they ended up going with a non-immutable distro. They say their Debian-derived system is as robust as Ubuntu Core, but seemingly immediately contradict this by saying they're using apt to manage updates.

Aren't they only using it for security updates though?

apt updates are not transactional, so abort the update mid way and you have a partially applied update. Hopefully the packager was careful enough to ensure your system still boots and reapplying the update cleans everything up.

You can make a boot-enviroment-snapshot for active/backup.

If anything goes wrong you boot backup, then again snapshot and repeat. That way you don't need anything more then apt/pkg etc.