Working in a multiplayer development environment can be extremely complicated, but I've spend time on every side of the infrastructure. I've ran my own backend servers that can deliver content to players, I've made desktop apps to connect to and control those servers, and I've made games making use of those servers!
If you need any packet of data sent, I'll have that thing on it's way in no time.
My largest multiplayer project was a brand new gamemode added to CraftyBoss's Super Mario Odyssey Online Multiplayer! In this mode the running team will need to avoid being frozen by the chasers, all while rescuing their teammates.
This includes an entire dynamic point scoring system and lots of synchronization between different gameplay clients. You can see the entire mode in action over multiple rounds in the video, which reached over 300,000+ views despite my channel being quite small at the time!