We have a REST plugin for Jira Server and I need to migrate that to the cloud. Is it possible to write a plugin that creates a new REST endpoint?
Unfortunately, not really. You can expose REST endpoints from your Cloud server/service, but it won’t be integrated with Jira’s authentication system (which identifies the Jira Cloud instance and its users).
See [AC-2515] REST endpoint Connect module type - Ecosystem Jira for details.