Any ideas on how to allow players to post something in a game and other players can see that something without having to rejoin? (Like Instagram I guess?) Is that even possible? If yes, what are the steps to implement such thing. Any help would greatly be appreciated!
You could do this in two ways,
Use Roblox datastores (slow and tedious)
Create an external web server and use that as the back-end for your “live forum” (hard to create but easy to use)