In your portfolio's Dividends tab, an upcoming dividend only appears under “Announced dividends” once the company has announced it. This often only happens shortly before the ex-date or before the annual general meeting. The tab doesn't show estimated dividends. You can see the “Announced dividends” section with a Plus or Investor subscription.
For the announced dividend, Parqet calculates with the shares you hold on the ex-date.
Estimates based on past dividends are only available in the dividend calendar. For this, the security needs at least 1 year of dividend history.