Hello Stéfane,
I've noticed that while using `guix shell guix -- guix --version`, it works
fine:

$ guix shell guix -- guix --versionguix (GNU Guix)
1.4.0-23.843b85cCopyright (C) 2024 the Guix authorsLicense GPLv3+: GNU
GPL version 3 or later <http://gnu.org/licenses/gpl.html>This is free
software: you are free to change and redistribute it.There is NO
WARRANTY, to the extent permitted by law.

However, when it is the system-wide `guix --version`, it does not:

$ guix --versionguix (GNU Guix)
892a915c08736c873a950bb2b44a6d0f49aea1d2Copyright (C) 2024 the Guix
authorsLicense GPLv3+: GNU GPL version 3 or later
<http://gnu.org/licenses/gpl.html>This is free software: you are free
to change and redistribute it.There is NO WARRANTY, to the extent
permitted by law.

This is just me speculating, but I think that the script `build-aux
<https://git.savannah.gnu.org/cgit/guix.git/tree/build-aux>/git-version-gen
<https://git.savannah.gnu.org/cgit/guix.git/tree/build-aux/git-version-gen>`,
which is supposed to set versions from the most recent annotated tags,
isn't working the way it is supposed to be, at least while building the
system-wide guix command.