Hello, I am one of the openHAB JavaScript library maintainers.
Your autocompletion works as supposed, we are missing type definitions for RuleBuilder because they currently don’t work properly and due to the complexity of RuleBuilder we weren’t able (yet) to provide type definitions for it.
Also see Require("openhab").rules is not exposing rule-builder methods / Typescript - #2 by florian-h05.
We improved the docs a few days ago to inform the users that we are missing type definitions for Rule Builder.