Hi Hans,
which version of lb are you using?
I am using the version from the Debian package live-build from "bookworm":
$ lb --version
20230502
The first thing I learned with that version from "bookworm" was that I
had to set all config directives regarding the distribution to
"bookworm" because lb from "bookworm" otherwise builds live images for
"bullseye".
Maybe your lb got an update and builds for "trixie"?
Matthias