
Hi @Soeren,
From the Formatting column with long text to multiple-line with word wrap site:
Rich text fields return their values with HTML. List Formatting automatically escapes values meaning that these types of fields will include HTML in their text values and that HTML will not be used as part of the page. It is not recommended to use rich text fields with List Formatting.
If you turn off "enhanced rich text" the JSON will work as advertised. Also declared in this article from MS for your reference: Supported column types.
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