Hi Wookey!
>OK, but you have to build new packages in a sid chroot too to check
>they work, as that's the suite they get uploaded to. It's fine to
>package in such a way that the package also builds in buster, but the
>primary target of a new package in debian is always sid (unstable).
So I can target debhelper-compat 12 to keep it buildable on buster or I shoukd strictly go with 13 as Mattia suggested?
Developer 13 is available in buster-backports.
Since updates as such the ones you are proposing need to go -backports, they can't go to the main suite, you can rely on packages that already in bpo.