green square?

It means the were recently logged in and are potentially still on.

https://support.chess.com/customer/en/portal/articles/1444855-what-is-the-difference-between-the-green-and-orange-square-on-my-profile-picture-

None of these answers make any sense. Can you play  against someone offline? Why won't the devs respond?

What do you mean exactly? If you mean on the same device, there is the Pass and Play option on the apps.

About devs not responding, probably because there are thousands of suggestions/reports incoming each day and the devs also have lives outside of chess.com. Most often it takes a few days to get a response.

However if you really want to know the answer and you ask kindly then some people may help you out on the forums.

Green square = online.

Use in live chess. If someone in my friend list is online I might challenge them to a game.

Use in daily chess (1-3 days per move). Daily chess is like old-fashioned correspondence chess in which special postcards were used to play matches with distant opponents. When I'm playing someone this way and I see the green online indicator, I'll stay online for a few extra minutes to see if they make their move while I'm logged in.