Check if these admin templates meet your requirement:

https://github.com/topics/react-admin-template

https://github.com/Kuzma02/Free-Admin-Dashboard

https://github.com/coreui/coreui-free-react-admin-template

https://medevel.com/os-react-dashboard/

Extras:

You may also check out these templates. They are not admin templates but may be of use for other projects:

https://reactjsexample.com/24-best-free-open-source-react-portfolio-page-templates