I can't say for sure that this is your problem, but it's the first thing that pops out when I look at your code.

The syntax for passing subroutine parameters in Tk is slightly different form the standard Perl method.

Try removing the () fromm the params, and separate them with commas. Like:

sub{[&createAccount,$txtNewUName,$txtNewName,$txtNewPassword]}
[download]

To check what is getting thru, print @_ in your sub. Like:

sub createAccount {
  
   my @in = @_;
print Dumper(@_);
     

   my(    $Username_arr,
       $Name_arr,
       $Password_arr,
       $PassCheck_arr,
      ....
     .....
     .....
}
[download]

You should start to see what is going on.