I don't know if it's intended like that (and so there's an error on the web site) or if it's a bug from the QMK implementation :
With the QMK implementation on EZ mode with Vim variant, accessing the Fn/Media layer is done by holding nav then holding ctrl, not holding nav then holding super like shown on the web site (doing the latter activates the Numrow layer).

I don't know if it's intended like that (and so there's an error on the web site) or if it's a bug from the QMK implementation :
With the QMK implementation on EZ mode with Vim variant, accessing the Fn/Media layer is done by holding nav then holding ctrl, not holding nav then holding super like shown on the web site (doing the latter activates the Numrow layer).