ALL Airbus illustrations show feet up on the pedals. On Airbus WIN, the most recent video also recommends feet up. Only one not so recent video from one test pilot says they don’t have a clear answer but all the newest videos on the subject recommend feet up.
FCTM says your feet must be in a position to be be able to apply full rudder deflection combined with braking even differential without delay. It’s impossible to do that with heels on the floor. Period. There is no possible argument about it anymore. Feet up is the way that Airbus recommends. It’s written black and white and it’s recommended in the latest Airbus WIN Videos.
That google Drive document is trustworthy as most of its content come from Airbus official documents such as FCTM FCOM and Airbus Safety First Magazines.