The bacport submissions are not really working with the factory version:
openSUSE_Backports_SLE-15-SP5_Update ppc64le unresolvable:
nothing provides libpng-devel >= 1.6.35
(got version 1.6.34 provided by libpng16-compat-devel)
(got version 1.2.57 provided by libpng12-compat-devel)
they need to be relaxed I guess.