@jacket97
The steps to create components in AEM forms remain the same as we have for AEM sites.
Once the custom component is created or if you want to add a new component to the list, you need to edit the template for that adaptive form in "Structure" mode and open the policy for the layout container. Once done, you'll have the list of allowed components for the templates.
You can create a new or existing policy, add new components to the allowed components list and save the template. Make sure the template is enabled.
Then, you should be able to get that component in the list when you create an adaptive form.
Hope this helps!