Jira - can't search with the quick filter for custom free text fields

Hello, I would like to search with a quick filter for custom free text fields in Jira, but it seems like this is not possible.
I tried it that way in a quick filter:

Custom free text field = XYZ (XYZ is the value I am searching for)

Could you help me, please?

Custom fields that are not available in all of your projects, can’t be searched via quick search without restricting your search on a specific project. That means you have to restrict your search or filter on a project.