That’s the strange thing. I used the repository installation method and it didn’t create the proper user. OpenHAB starts up and runs just fine. I may not have it running as root though. Last time I installed on the Pi so I think the permissions may have been slightly different.
But you are correct, I open the addons.cfg file but from the repository installation location. Then in the persistence section I add the line above just as you entered it. I don’t know if the repository didn’t install correctly, if I missed a step, or if I have to adjust OpenHAB to run as root.