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You can't send reminders to “project roles” and direct e-mail addresses in the cloud version of the app.
There are no JQLs for finding issues with reminders. Currently, this is not possible with the Forge Platform.
There is no option to configure reminder email/message template.
Advantages of Cloud Version
You can send reminders to Slack workspaces in the Cloud version. This feature is not available for Server/DC versions.
Reminders are also available in the customer portal for customers.