Perl 6 formats aren't like Perl 5 formats. They're much more dynamic. And available in Perl 5. Try this:

use List::Util qw< max >;

my $terminal_cols = 80; # or whatever
my $column_gap    = 3;  # or whatever

my @display_items = map { "$_: $hash{$_}" } sort keys %hash; 

my $max_col_width = max map {length($_) + $column_gap} @display_items;
my $column_count  = $terminal_cols / $max_col_width; 
my $formatting    = '{:[[{*}[[:}' x $column_count; 

use Perl6::Form; 
print form $formatting, (\@display_items) x $column_count;
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