Dynamic Queries with Projection

I am trying to create an API like graphql in .net core. i have created a dynamic filter based on the input fields as well as added dynamic projection based on the fields required to return in the response. I am trying to add one more array of objects inside the document. But this array will be get updated frequently.
Will it be fine to keep this array inside the same collection or different collection?
If it same collection then create and update that will happen in the same collection will it impact any performance because I will have 10 million documents in the collection?
I am using azure cosmos DB so it have a separate region for the read. so get will not be affected.