Strapi's roles on Mongo Atlas, Full cluster access?


I’m using strapi with mongoDb Atlas.
On my Atlas’cluster i have sereral database, To secure my strapi database, I want to give it access only to its database

If I restrict the roles (full role) to the strapi database, it doesn’t work

But If i give full roles to my cluster (all database) is working

Why do you need full access to my cluster?
Can you tell me which roles I need?

Thanks you for your help