We can confirm that in order to migrate to ScriptRunner for Jira Cloud from ScriptRunner for Jira Server or Data Center that we have created a Migration guide located in the documentation page here.
The migration guide explains the strategies that should be used to rewrite the ScriptRunner for Server Scripts which use the Java API to use the Rest API's which Jira Cloud provides to make them compatible with ScriptRunner for Jira Cloud.
We would also advise reading through the documentation page which we have produced and is located here as this explains the differences between the Server and Cloud versions of ScriptRunner.
We would advise reading through this as the Cloud version is different from the Server version, and this page will help you to identify any functionality that you may lose when migrating to the Cloud version.
It is important to note that there is no automatic migration path from Server to Cloud so you will need to follow the steps in the migration guide in order to rewrite your scripts and to migrate them to ScriptRunner for Jira Cloud.
It is also important to note that not all of the features inside of ScriptRunner for Jira Server or Data Center exist inside of ScriptRunner for Jira Cloud due to the differences in the API between the Cloud and Server versions, so we would advise reading through the page linked above explaining the differences so you can identify what functionality may be lost when migrating to ScriptRunner for Jira Cloud.