This looks at first glance like a genuine bug in the PDL distribution
The OP's problems are with some PDL::Graphics modules, but PDL is working fine. The PR you refer to was to make PDL::Graphics::TriD build on MacOS, which the OP hasn't tried.

Gnuplot is fiendishly hard to interact with programmatically, because it requires talking to an executable over a pipe. This makes it prone to all sorts of cross-platform problems.

In reply to Re^2: Missing sub-module of PDL::Graphics::Simple by etj
in thread Missing sub-module of PDL::Graphics::Simple by perlboy_emeritus

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