In the Jira Cloud Migration Assistant, currently all users & groups are migrated. This does not provide the flexibility needed to only migrate a sub-set of users the customer deems is approved or needed to be given product access in Jira Cloud.
It is possible to contact Atlassian Support to ask that we disable the user & group step and perform a manual user & group migration (see this comment). This then allows a migration option where
- The first migration requires all users & groups to be migrated (end users are not notified of this event).
- Remove the users and groups not needed in Cloud
- Disable user & group migration in the Jira Cloud Migration Assistant
- Migration of projects then only adds project config, issues and attachments. Users and groups remain as per the manual overrides performed in the previous steps.