RaspPi 4, „current“ firmware as of 2/12/2020, Max2Play 2.51, standard Max2Play image without „apt upgrade“. 32-bit kernel, HDMI highres audio not enabled. Pretty much „fresh out of the box“.
When I attempt to set HDMI-Mode to „HDMI“ and click „Save“, HDMI-Mode will be set to „DVI/VGA“. Setting it to „DVI/VGA“ does the same, this is not a case of the two options simply being switched when saving.
Happily, HDMI output works with HDMI-Mode „not set (default)“.