Unable to extract date from file name

In fact I would like this date the be fullfill this way
Not to create a new custom data but convert in real date.

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I’ve already suceed to create this … But unable to convert nor this or directly part of the file name into a real date

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Actually I’ve only found this but can’t change date using filename

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Maybe it is just not possible to transform 8 digit in date. Sad about this. None of previous thread found the answer.