This is a simple minecraft spigot/paper plugin for 1.16+ in which all players share a single inventory basically if you pick up a block every player will have that same block in their inventory in the same slot if they place it it will be removed from everyone same goes for durability of tools or enchantment and if someone dies the items will be removed from everyone and dropped where that player died.
There are 2 commands :-
startsharedinventory - by default if you put the plugin a server it will be started but if you stopped it for some reason you can start it again by this command
stopsharedinventory - to stop the sharing of inventory for any reason.