Hi Gunnar,
So now you have two options:
1. Ask the release team for an unblock
https://release.debian.org/testing/freeze_policy.html#appropriate
2. Leave it as is, and let it stay at version 16.0.138-4 in Debian 12.
I uploaded 16.0.139-2 to mentors which excludes building on s390x. We
changed that a year ago to build on "any" after a discussion on the
Debian Input Method mailing list
<https://lists.debian.org/debian-input-method/2022/03/msg00095.html>,
but it turns out that Keyman is actually not working on s390x
because it doesn't yet support big endian architecture (see upstream
bug #5111 <https://github.com/keymanapp/keyman/issues/5111>) - a fact
I had forgotten back then. So I hope that's an acceptable option in
addition to the two you listed 😁.