I think it's always been assumed that breathable air can pass through the walls of a wall of force
, because otherwise you'd have to pull up the suffocation rules and do math to determine how much air is already in there
. Since cubes of force
are basically those spells in item form, I'd say... it's up to you. The reddit link above says that there would be about 8 hours of air in such a cube, even if no new air enters. And since each charge lasts for 1 minute...
So, as evilly dramatic and cool it might be to suffocate someone in a pitch-black cube of force
, it's likely not actually possible. Sorry.