Currently, there are no specific search templates for custom fields created with JMCF; currently the only search template available is Forge custom field searcher, the default search template for Jira Forge apps. Because JMCF uses native data types, the fields are generally searchable using JQL and basic search. However, there are some limitations:
Time in Status can only be searched by number of seconds.
Search template flexibility will be expanded in later versions of JMCF for Jira Cloud as the Forge team introduces more capabilities for search.