Just hilarious😂!

Well got impatient & could not wait for a clue, so looked in /usr/local/lib/perl5/5.36/Getopt/Long.pm, there saw "prefix="(💡) ...

1335 # Getopt::Long Configuration.
1336 sub Configure (@) {
...
1423         elsif ( $try =~ /^prefix=(.+)$/ && $action ) {
1424             $genprefix = $1;
1425             # Turn into regexp. Needs to be parenthesized!
1426             $genprefix = "(" . quotemeta($genprefix) . ")";
...
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... So I had failed to use = as a option-value joiner that the doc says nothing about (all it has about configuration: This subroutine takes a list of quoted strings, each specifying a configuration option to be enabled). Obviously🙄