It sounds like an unusual way of doing things, so maybe you should explain the broader context for your question, but to answer it you'll notice that in GetOptions( 'arg1=s' => \$arg1); there are no quotes around the second argument. You shouldn't have quotes in your other attempts (ie, instead of sending a string, send a reference):

my @opt = ('arg1=s', \$arg1);
my %opt = ('arg1=s' => \$arg1);
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