So after finding out about the multiplayer feature, I was just wondering how far it could go. So what would be the maximum amount of people that could join a single room?
To preface this comment, let me just mention. I've never done full online multiplayer with Construct 3. But, I have with other Game Engines/Programming Languages. And, have also run multiple private servers for various online games, from my home computer/network, and on shared or dedicated servers over the years.
Just Reading through the Multiplayer section of the C3 Documentation. It seems to me the maximum amount of people who could connect, would depend on multiple things. The type of game, and who is actually hosting the room for the game. If the Room is hosted on a Dedicated Server, this looks like it should support high latency/latency-sensitive games to run much better.
So two things to consider, how much information/data your game is transmitting over networks. And the actual power, and connection speeds of the host of the game. Whether that may be on a personal computer, or on a professionally managed dedicated server for online gaming, and anything in between.
EDIT: I meant to mention that there are Addons, such as the "PlayFab" Suite of Addons, which adds a lot of functionality to online/multiplayer games developed within Construct 3. Including, Photon Realtime, which is a well known cross-platform networking engine. Which folks have been using alongside various game engines to create online games for a while now.