I'm altering the code so that portals can only be build and used in specific worlds.
Should the config option be active-worlds or the negated form disabled-wolds?

Personly I would prefer active-worlds, but then ofcourse it would break existing setups.

So 2 options:

1. Use disabled-worlds
2. If no worlds are set with active-worlds, every world is allowed

Why not just not give the create/use permissions in those worlds?

Indeed, thats an option with plugins like LuckPerms 👍