push up for your own body weight is not heavy enough to strain your muscles. if you are a reasonably fit person, it won't help you to grow even if you do 100 push ups daily

correct . at best you will only maintain your current mass. impoosible to grow using pushups.

even assuming the gyms open on that day, i forsee there would still be strict rules imposed

i guess most people muscles have shrunk during 6 weeks lock down