Can i use my own UI in openhab

hi guys
can i integrate my own ios app within openhab i create UI/UX

Welcome to the openHAB forum!

Yes, using REST calls will enable you to build your own UI.

what about the api how i would call them bc my application base in node.js

You cannot call java API from javascript if one process is in the JVM and the other one in NodeJS. That would only be possible if both are running in the same virtual machine like GraalVM (not supported by openHAB).

Use the Http based API as interprocess communication.

Your plan also doesn’t make sense IMO. You don’t need nodejs for your own UI. Just a normal webpage/javascript or a native iOS app that directly accesses the Http API.