Form validation for three form fields, requiring at least one to be filled in – issue with “null” and “empty”

Help
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1

If I understand correctly, only the fields specified by the validation rule are allowed to be saved. I have 3 form fields, at least one of which must be filled out, and I don’t know how to write the validation rule correctly in JSON so that the user receives a notification both when creating the record and when editing it.
As a test, I tried having all three fields empty, and this validation rule actually works (entered as raw JSON under “Validation”):

{
    "_and": [
        { "Kontaktperson": { "_empty": true } },
        { "_and": [] },
        { "Institution": { "_empty": true } },
        { "_and": [] },
        { "Zustaendige_Naturschutzbehoerde": { "_empty": true } }
    ]
}

The problem arises when I want to specify that at least one of the three fields must be filled in; I thought it would work like this:

{
    "_and": [
        { "Kontaktperson": { "_nempty": true } },
        { "_or": [] },
        { "Institution": { "_nempty": true } },
        { "_or": [] },
        { "Zustaendige_Naturschutzbehoerde": { "_nempty": true } }
    ]
}

… but nothing happens, and the rule doesn’t apply at all.

Or do I need to nest all the cases that should be allowed into multiple OR statements so that they are applied as an AND rule overall? How do I set the rule correctly so that Directus (11.1) checks that at least one of the three fields is filled in?

Thank you very much for any help or advice