first of all variables that will be shared between threads needs to be shared so hash transaction_hash needs to be declared as well as shared. Second you need to pass the %transaction hash as a reference into %hsh with the \ prefix. Look at the following code

#!/usr/bin/perl -w
use strict;
use warnings;
use threads;
use threads::shared;
use Data::Dumper;

my %hsh : shared;
my %transaction_hash :shared = ( 'another_k' => 'another_v');
$hsh{inner_hash} = \%transaction_hash; # referencing

my $thread = threads->create( \&subrt, %hsh );
$thread->join();

sub subrt {
    my %args = @_;
    print Plugin->execute(%hsh);
}

#Code for Plugin module
package Plugin;

sub execute {
    my $class = shift();
    my %abc   = @_;
    my %shsh  = %{$abc{inner_hash}}; #dereferencing
    foreach (keys %shsh) {
        print $_. "---" . $shsh{$_}."\n";
    }
}
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