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Set up a headless Factorio server (using this factorio docker image) and then expose a connection to that via a Tailscale tailnet. Then use share URLs for that node to give your friends access to the tailnet. Those friends will each have to have their own tailnets which is how access is identified and shared.

Also, it took some digging and I finally found a normal video of a few people demonstrating what multiplayer (co-op) Factorio looks like -> youtube