Generally MMOs are a lot harder to create than other games because they require significantly higher funding for servers, customer support, etc. The technology is also more advanced due to needing to program both a server and a client, and making them communicate effectively.
Your best bet would be to use an already existing engine, or making a Graal server. You can rent a Graal server for like $120 a year, and youc an make your own levels and script things fairly easily. It probably won't get many players unless you can somehow convince talented people to help you, but it can be a fun experience building a world, programming things, and you learn a lot about coding. It's how I first got into programming.