The tutorial about multiplayer game uses a Network extension, which is not available with GDevelop 5. That extension is available in C++ format on GitHub. How can it be added (imported or installed) to a new game in GDevelop 5?
Old extensions are not compatible with current version of GDevelop5.
Your best hope is @arthuro555, he can say more about it.
I will let him explain you what he will building about multiplayer 
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Ok basically, I will add a socket io client extension and add features specific to GDevelop to make multiplayer easier. This will not come out soon though. I don’t have much time lately sadly.
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Thanks Arthuro, good to know. I’m a real newbie at GDevelop (about two days into it) and really like it, so far. If I come up with something before you (unlikely) I’ll share 
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