Similar story to me a few years later. I starting out by hosting a Lineage 2 server emulator back around 2005. Slowly got into tweaking a few things, debugging performance issues, eventually writing whole new features. Learned a whole lot about databases from that experience so in 2010 at my first helpdesk job, they found out "you know SQL?!"...so I then was given a ton of reports to write, and quickly a whole lot more responsibilities, launching my career into databases.
While working as a data analyst a few years later, I wanted to improve my programming skills. So as a side project I did a whole lot of work on a ground-up rewrite for a year or so...I had reimplemented: player and npc movement code, npc spawning, a basic AI system (attack, flee, loiter, travel), pathfinding, inventory and equipment slots working, item drops in the world and being able to pick them up, chat (direct and global), and probably a few more things I can't remember!
I was pretty uninterested in the actual Lineage2 gameplay at that point, so I was trying to get the basics working so I could implement a more interesting combat system / skill tree. The game engine had some extreme limitations on what you could actually control just from the server side, but I had a system working that repurposed a news bulletin UI that the engine had in-place to inject some custom HTML based UI's that I could send over from the server. So I was able to disable the existing skill tree UI and inject my replacement system that I was designing.
That project got put on hold when I decided to start my company in 2015. It was amazing for learning, because I was actually interested in it. As I got older, my interest in gaming and gamedev have both waned. No interest at all in going into that hyper competitive market!