Available to the extent allowed by Cloud limitations.
Workflows Post Functions
JQL Keywords vs JQL Functions
A JQL function performs an evaluation of the issue in real-time during the JQL search. This search type is not possible in Jira Cloud because it is a very resource-intensive search.
A JQL keyword is meta-data for an issue that has been evaluated and saved prior to a JQL search. This search type is available in Jira Cloud. It is faster and more efficient than a traditional, functional search because the results can be indexed and it is less resource intensive.
Live Fields (screen manipulation)
The solution is currently in development. It will be available soon with limited support and to the extent allowed by Cloud limitations.
Conditions/Validators
The only solution available for custom workflow conditions and validators is through the Atlassian Expressions language which has limited functionality compared to SIL.
Routine Availability
No Cloud API support is available for all routines in Server. Some routines are currently in development and will soon be available in Cloud. The actions for the unavailable routines are still supported using the REST API.