Is it possible to duplicate users on a new WordPress install?

Migrate DB Pro can help with this, make sure to migrate any plugin tables and the WP_Users and WP_Usermeta tables if your users make posts and you want that content to remain assigned an available make sure to keep WP_Posts and WP_Postmeta table as well.

https://deliciousbrains.com/wp-migrate-db-pro/

Also keep in mind that WP uses an EAV (Entity Attribute Value) architecture for pretty much everything User and Content related so if you have a ton of users it will take time or possibly crash.

I run a site with 100K registered users and I have no problems with this process using MigrateDBPro but I know that larger sites would have problems.