I found two issues when trying out the demo.

Install instructions:

Following the install instructions verbatim doesn't work (as of 05:00 EST, Feb 16). The quickest and easiest fix was to run 'jump ff_bar_demo' without the '_screen'

I imagine this is because you can't jump to a screen; you have to 'jump' to a label and 'call screen' a screen.

Exception: (Occurs in both Ren'Py 8.3.2 and 8.3.4)

While running game code:
    File "game/freeform_bar_demo/ff_bar_demo.rpy", line 51, in script
      call screen ff_bar_demo_screen
    File "renpy/common/000statements.rpy", line 671, in execute_call_screen
      store._return = renpy.call_screen(name, *args, **kwargs)
    File "game/00freeform_bar.rpy", line 77, in render
      r = renpy.Render(get_size(self.mask)[0], get_size(self.mask)[1])
 NameError: name 'get_size' is not defined

I don't know how to fix this one off the top of my head. I assume that you expected the pygame library that's imported at the top of the file to contain 'get_size', but it's not working.

I experienced a similar issue with your radar chart asset a few months ago, where 'math' was not defined when trying to use 'math.pi'. Changing 'import pygame' to 'import math' worked as a fix there, but not here.