While manually fixing this on my laptop, I noticed some more differences
upgrading vs fresh install:
https://sources.debian.org/src/systemd/257.9-1~deb13u1/debian/libnss-systemd.nss
https://sources.debian.org/src/systemd/257.9-1~deb13u1/debian/libnss-mymachines.nss
https://sources.debian.org/src/systemd/257.9-1~deb13u1/debian/libnss-myhostname.nss
bash5$ sudo GIT_PAGER= git -C /etc diff -U0 --word-diff nsswitch.conf
diff --git a/nsswitch.conf b/nsswitch.conf
index b4e7b91..cac7bc6 100644
--- a/nsswitch.conf
+++ b/nsswitch.conf
@@ -9,2 +9,2 @@ group: files systemd winbind
shadow: files {+systemd+}
gshadow: files {+systemd+}
@@ -12 +12 @@ gshadow: files
hosts: files {+myhostname+} mdns4_minimal [NOTFOUND=return]
{+mymachines+} resolve [!UNAVAIL=return] dns[-myhostname mymachines-]
