One of the reasons for running this site is just the mundane checking that system upgrades won’t break anything.
The underlying droplet is essentially still a running OS, but there’s no way to upgrade it and test, then roll back in the event of a failure, without backing up and restoring snapshots etc.
All doable, but hardly fun.
The easier option is just to upgrade a test server first, which is this one.
So far an “apt update” followed by an “apt upgrade” and a reboot seems to have gone fine.
Publishing this post will be the next test.