Currently, there is no way to retrieve the Creation date of Projects, and this would be helpful if the following endpoint return the Creation Date:

https://developer.atlassian.com/cloud/jira/platform/rest/v3/api-group-projects/#api-rest-api-3-project-projectidorkey-get

Workaround:

• You can create a cloud backup of the Jira site using the steps here - Export data from Jira Cloud. The entities.xml file will contain a list of all projects, including metadata that includes the creation date.