Date has wrong format when booking in bank account as paid

That is a field to hold the reference of the invoice number that is being paid - not a date field

That’s right.
But the default date notation is set to dd-mm-yyyy.
The user now thinks that the invoice has as date 04-01-2021 when it should be 01-04-2021. So for the user this is very confusing.

Is there a purchase invoice with that reference number?

Yes there is.

The problem is not related to just that invoice (202150260).

If I want to add a payment of an invoice, I get this listing, which is hard to read:

After clicking on one invoice the listing changes, and is more readable.

But as you can see, the dates shown are not in accordance with the Date&Time setting in [Settings].
Should be dd-mm-yyyy in stead of mm/dd/yyyy.