Thanks. After starting to check some semi-random things, I found that once I added imagemagick-svg and imagemagick-webp to that system the script resumed working. So, at the end of the day, the problem had nothing to do with Perl except that the symptoms of some change manifested via well-used Perl script on a production system which has only received system updates of late. Unfortunately I have no clue as to what or why there were changes inside those updates which set the script off its rails.

tldr; solved but dunno the original cause

In reply to Re^4: Image::Magick - Exception 435: unable to open file `Image::Magick::Q16' @ error/Q16.xs/XS_Image__Magick__Q16_Read/13529 by mldvx4
in thread Image::Magick - Exception 435: unable to open file `Image::Magick::Q16' @ error/Q16.xs/XS_Image__Magick__Q16_Read/13529 by mldvx4

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