In MongoDB, a single document can have up to 64 indexes, which include both user-defined and system-defined indexes.
However, it's important to keep in mind that creating too many indexes on a document can have performance implications. Indexes consume storage space and can impact the performance of write operations such as insert and update, as well as read operations that involve index scans.
Therefore, it's important to carefully consider your indexing strategy and choose the indexes that will provide the most benefit for your application's queries. It's generally a good practice to only create indexes that are necessary for the most frequently executed queries and to periodically review and optimize your index usage as your application's data and query patterns evolve.