Currently, when using Workflows with a "Form Submitted" trigger, we can:

Map form fields to Contact fields and to a Custom Object (in my case, a Custom Object called "Mandate").

Create or update an Opportunity using the "Create/Update Opportunity" action.

Define many-to-many associations between Opportunities and the Custom Object (Mandate) in Settings › Custom Objects.

However, inside the Workflow builder, the "Create/Update Opportunity" action does not provide any option to:

Select a specific Custom Object record (e.g., a Mandate identified by Mandate ID from the form), or

Automatically associate the newly created Opportunity with that Custom Object record.

This means that even though the association type (many-to-many between Mandate and Opportunity) is configured, we can only link Opportunities and Custom Objects manually later from the record view, not automatically as part of the automation.

Requested enhancement:

Add support in Workflows to associate Opportunities with Custom Objects at creation time. For example:

In the "Create/Update Opportunity" action, allow selecting a Custom Object association field and mapping it from:

A Custom Object record already in context, or

A field value (e.g., Mandate ID) that can be used to look up the correct Custom Object record.

Alternatively or additionally, provide a dedicated action such as:

"Associate Records" that can:

Take the Opportunity created earlier in the workflow, and

Associate it with a specific Custom Object record (e.g., Mandate) based on a field like Mandate ID or an existing association on the Contact.

Why this is important:

Many businesses use a Custom Object as the core entity (e.g., Mandate, Project, Case, Policy, etc.).

Forms often collect both Contact data and a reference to that core Custom Object (like Mandate ID).

We need to automatically tie the new Opportunity (deal) to that Custom Object in the same workflow, without manual linking.

This would make Custom Objects, Opportunities, and Workflows work together seamlessly and reduce manual work and data inconsistency.

Example use case:

Custom Object: Mandate (a business I am selling).

Form: collects Contact details and Mandate ID.

Workflow:

Trigger: Form Submitted.

Action: Create/Update Opportunity.

Desired behavior: Automatically associate the new Opportunity with the Mandate record that matches the Mandate ID from the form, so Contact, Mandate, and Opportunity are all linked together via automation.