Here’s what the Flux documentation says about creating a custom component:
"Learn how to create custom components from scratch in Flux, giving you complete control over your component library.
In this tutorial, we'll cover the complete process of creating custom components in Flux. You'll learn how to create each element of a component, from terminals and symbols to footprints and simulation models, and finally how to publish your creation to the library for future use.
This guide covers the following topics:
Creating a part schematic with terminals
Creating a custom symbol
Creating a custom footprint
Adding a 3D model
Creating a simulation model
Publishing to the library
Parts in Flux are made of 5 main components. All these components are optional, but a part missing a component won't offer its full capabilities:"