Hello @Santosh Kumar Singh ,
Welcome to the MS Q&A platform.
In cosmos DB, the system function -count(scalar_expr) will benefit from a range Index for any properties in the query's filter.
Below is the document explaining the include/exclude index strategy.
https://learn.microsoft.com/en-us/azure/cosmos-db/index-policy#includeexclude-strategy
I hope this helps. Please let me know if you have any further questions.