This is not a stupid question asking members of the forum how to create a multiplayer game. All I want to know is if it is at all possible to make a construct game multiplayer.
Not yet, although we have plans to eventually support it.
Would it be possible through external code after export?
If you are good with server side codes, there's a few examples here in the forums of a few members who managed to get multiplayer working, at least on LAN.
Here's a good recent example by Juantar.
Develop games in your browser. Powerful, performant & highly capable.
If you're a good javascript programmer and want to start making it yourself with WebSockets, you can do so already with the Javascript SDK.