A'llo, there are multiple solutions you could use.
1. Create a
called by other action in the actions tab section for the scene & rename it to something relevant like: "check_items", now add some action parts along the lines of this to it - I'm just going to assume that you are using conditions to update when the player has picked up the relevant items.
if condition "item1" is true
if condition "item2" is true
if condition "item3" is true
if condition "item4" is true
set condition "door_visible" to true
end if
end if
end if
end if
The general idea behind this solution is that each time the player picks up an item you use the call action action part & call the called by other action you just created, which will then check if all of the conditions are met & if they are then the door should be unhidden.
2. A more ideal solution would be to link a value to the door instead & increment the value by 1 each time one of the items is picked up & put into your inventory. Values are a lot more flexible than conditions because unlike conditions which can only return true or false, values can check if the value associated with it is: equal to, not equal to, greater than, greater than or equal to, less than, less than or equal to, etc. which makes them really good for objects/puzzles that contain multiple states.
Think of states along the lines of this: you have a door, the door is locked (1). The player finds a key & uses it to unlock the door. The door is now unlocked, but it's still closed (2). The player opens the door. The door is now open (3).
Quick note: you mentioned that you have watched some tutorials, so I am assuming that you already know how to assign conditions or values to scene objects to control whether they are visible/active or hidden/inactive.
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