External Elasticsearch and Nextcloud

Hello Nextcloud Community,

this might be a stupid question, but I can’t seem to find the answer by my self.
I want to use a single Elasticsearch Server for multiple Nextclouds.
I set up a Nextcloud on an apache2 Webspace. Then I wanted to configure the fulltextsearch, for that I need the ES instance. I installed ES on a new VM and after setting up I tried to connect em via a specific User. The Problem is if I don’t give the role this user has the rights to access the cluster via cluster privileges, Nextcloud just prompts BadRequest. If I give the role specific cluster privileges , for example “monitor” it runs smoothly. Now I suspect Nextcloud needs some cluster level privileges to index but which one and why?

English isn’t my primary language, I apologize in advance for any weird phrasing.