%handler_for is a hash, $action is a scalar.

The value of $handler_for{$action} is either a coderef (a pointer to a sub) or if this is no-strict-refs code perhaps the name of a function as a string.

&{ $handler_for{ $action } }(%opts) calls that function, passing it %opts as an argument. An alternative, perhaps clearer way of writing it might be:

   my $function = $handler_for{$action};
   $function->(%opts);
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