It is possible to use references as values in a shared hash, but you have to also share the reference.

use threads;
use threads::shared;

my %h : shared;
$h{test} = [];

Invalid value for shared scalar at (eval 4) line 1, <> line 4.

my $ar = [];

$h{test} = $ar;
Invalid value for shared scalar at (eval 6) line 1, <> line 6.

share $ar;

$h{test} = $ar;

## No error this time.
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You could also do this as

use threads;
use threads::shared;

my %h : shared;
my $ar : shared = [];
$h{test} = $ar;
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Or even

use threads;
use threads::shared;
my %h : shared;
my $ar = [];
$h{test} = share( $ar );
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but the attempt to cut out the temporary variable and write

use threads;
use threads::shared;
my %h : shared;
$h{test} = share( [] );
Type of arg 1 to threads::shared::share must be one of [$@%] (not sing
+le ref constructor) at (eval 6) line 1, near "] )"
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gives an error because of what the threads::shared pod terms "perl's prototyping problems" :)