JCMA migrates few workflow rules that belong to Marketplace partner apps on server side as a native workflow rule to Jira Cloud. Here's the list of such workflow rules,

https://confluence.atlassian.com/cloudkb/workflow-rules-migrated-via-jira-cloud-migration-assistant-1031838515.html

Migration of these workflow rules will fail if its configuration contains references to Jira Service Management custom fields that are not supported by JCMA.

We've received a request from a Marketplace partner to support this use case. Here are the samples of such custom fields,
com.atlassian.servicedesk.approvals-plugin:sd-approvals
com.atlassian.servicedesk:vp-origin
com.atlassian.servicedesk:sd-customer-organizations
com.atlassian.servicedesk:sd-request-participants
com.atlassian.servicedesk:sd-request-feedback
com.atlassian.servicedesk:sd-request-feedback-date