I confirm the message of libpng. But this derives from the fact that I compiled XOrg packages (and needed dependencies) using the package versions included in pankso's wok during the first run.
Since I experienced problems between gcc10.2 and some of the packages, I switched to newest versions one by one.
This lead to my mistake that I compiled some packages with libpng1.2 and sometimes later others with libpng1.6. So if libpng-xx.tazpkg is updated, the earlier versions don't find the expected dependency anymore. This is no error of the slitaz scripts but my mistake.
This is why I started a new run, compiling the packages again from start along the Linux-From-Scratch (LFS) - Beyond-Linux-From-Scratch (BLFS) order, hoping to prevent this from happening again...
As far as I can see up to now, the resulting packages are roughly in the same order of magnitude as the x32 packages. Therefore I hope to achieve a x86_64 system maybe 50% bigger than the 32bit variant.
Any "normal" distribution (knowing well that there are other "tiny" Linux Versions than SliTaz) I know comes down by at least ~1GB of size, while slitaz 32bit runs with a "installed" system of ~170MB. To my understanding, this is a result of the strict modularity, where single libraries are extracted from fullblown packages, leading to some 100 kB of size where a full package (used by other distros) would be in the MB region (correct me if I'm wrong...).
So: no surprise that a LFS system is well beyond 1GB but that does not (yet) destroy my hopes for a relatively small x86_64 SliTaz...