Are you sure that's the code you ran? It should work. And it works for me.

>perl 655812.pl
superclass hello
make a window
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use Object::Tiny qw(dummy);
can be written as
use Object::Tiny;
but not as
use Object::Tiny qw( ); or
use Object::Tiny ( );
You would get the error you showed if you did one of the latter two.

Also, if you have no members, you can use
$ui = 'UI'; instead of $ui = UI->new();, and
$ui = 'UI::Graphical'; instead of $ui = UI::Graphical->new();.
However, you'll probably need some members, so you might as well continue the way you are going.