Hi @Kim_Hakseon,
I’m not aware of a specific limit on number of shards. For a similar discussion on limits, please see my response on Database and collection limitations - #2 by Stennie.
Practical limits you may encounter are documented on MongoDB Limits and Thresholds. Some limits vary between versions of MongoDB server, so make sure you are reviewing the manual version matching your MongoDB server deployment.
Regards,
Stennie