The 'x' operator can act upon strings or upon lists. The use above, "Hello" x 3" created three concatenated copies of the string "Hello", thus "HelloHelloHello". What you wanted was "three copies of an item in list context", like so:

my ( $var1, $var2, $var3 ) = ("Hello") x 3;
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The parentheses force the value into list context, the 'x' then makes three copies of that single value list, and you get ("Hello", "Hello", "Hello"), which is what OP wanted.