The Jira Cloud Migration Assistant (JCMA) supports the selection of dashboards with Custom Charts gadgets when migrating from Jira Server and Jira Data Center to Jira Cloud.
If you don’t want to use the JCMA, or you experience issues during the migration, you can move your Custom Charts data manually with the configuration import/export tools.
Additional information
Review Atlassian’s documentation for more details about the JCMA and the migration process: