local our %count;
$str =~ /
    (.+)    # or .{N,} where N is minimum length.
    (?(?{ $count{$1} })
        (?!)
    )
    .*
    \1
    (?{ ($count{$1} ||= 1)++ })
    (?!)
/x;

##</code><code>##

my $min_len = 2; # Substring is at least two chars long.
my $min_count = 3; # Substring occures at least three times.

local our %count;
use re 'eval';
$str =~ /
  (.{$min_len,})
  (?(?{ $count{$1} })
      (?!)
  )
  (?>
    .*?
    \1
  ){@{[ $min_count - 2 ]}}
  .*
  \1
  (?{ ($count{$1} ||= $min_count-1)++ })
  (?!)
/x;