can someone please explain what six and seven mean and why is everybody commenting that??

They don't really have a meaning, except the ones that were already explained in the manga (like 6 being an incomplete number for example). 7 and 6 is quite literally "Nana" and "Roku" in japanese, so those numbers fit the mc's.

Everyone is commenting 6 and 7 because it's brainrot. I had to search that up too haha