As mentioned by @Alexis Robert answer, it is my understanding that "issueFunction" usage is not an out of the box function. It is provided by a third party add-on "ScriptRunner for Jira". If you don't have it, then you will not have this function available when you construct your JQL.
Best, Joseph Chung Yin.
As an alternative solution, you can try Dynamic Filters: JQL Replacer for Jira. It allows filtering issues without JQL knowledge. For example, you can create such a smart field for your request and add it in dynamic filters. Also, you can save dynamic filters for Jira filters.
Hope it will help
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