Background from microsoft documentation:

The user attributes supported for a given application are preconfigured. However, some applications support custom attributes, and the Microsoft Entra provisioning service can read and write to custom attributes. To enter their definitions into the Microsoft Entra admin center, select the Show advanced options check box at the bottom of the Attribute Mapping screen, and then select Edit attribute list for your app.

Sign in to the Microsoft Entra admin center as at least an Application Administrator.

1. Browse to Entra ID > Enterprise apps.
2. Select your application, and then select Provisioning.
3. Under Mappings, select the object (user or group) for which you'd like to add a custom attribute.
4. At the bottom of the page, select Show advanced options.
5. Select Edit attribute list for AppName.
6. At the bottom of the attribute list, enter information about the custom attribute in the fields provided. Then select Add Attribute.
   
   Example: Here is what i can see in our SAP Litmos SCIM Config which is an app that allows for custom attributes

in Lucid this option is not available which I have been told by Austin Galura at Lucid the integration only allows for pre configured attributes. 

Request:

We would like to add additional attributes to the scim attributes we can configure in entra. See screenshot below. Currently we can only map upn, email, first name and last name. We kindly  ask for a new feature request to extend this to all of the attributes listed on the right side of the screenshot. Thank you!