Formatting Property Values XML View

Hey Experts,

I want to format two Fields of a Tabel which input Binding shows one time date in format yyyymmdd with out sepperators and i want to view it as yyyy-mm-dd so i've tryed it like the API told me but it get [Object object] in the column.

Here are Code snippets and view of the table:

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Regards,

Dominik Lückel