Fluent UI uses CSS-in-JS - We should opt for that as well.

Formik vs react-hook-form

Formik is older, components take longer to mount, re-renders the entire form on field change.
react-hook-form was written to replace Formik, better mount and rendering performance
Both Formik and react-hook-form have good community adoption (above 1mil npm weekly downloads)

Formik - https://www.npmjs.com/package/formik
Size - 13kB
GitHub stars - 28.9k
GitHub issues - 542
npm weekly downloads - 1.3m
Last publish 6 months ago
License - Apache License 2.0

react-hook-form - https://www.npmjs.com/package/react-hook-form
Size - 8.4kB
GitHub stars - 24.4k
GitHub issues - 0
npm weekly downloads - 1.6m
Last publish 5 days ago
License - MIT License