I agree, the documentation for that module is murky and confusing. I also played around with it for a while without success. DateTime::Event::ICal has a cleaner API for creating the DateTime::Set object. This replacement makes it work, leaving the rest of the original code alone.

use DateTime::Event::ICal;

my $biweekly = DateTime::Event::ICal->recur( 
        dtstart  => DateTime->today(),
        freq     => 'weekly',
        interval => 2,
);
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