There is a Jira Standard API available to validate a Project Key (GET /rest/api/2/projectvalidate/key).
As per our requirement, we need to create a jira project programmatically through api's, we need to validate Jira Project Name.
For Jira Cloud, API is available to validate Jira Project Name(GET /rest/api/3/projectvalidate/validProjectName).
Not sure why its not made available for server/datacenter even though its a a valid case and frequently needed when any project needs to be created using APIs.