Now I would like to add an additional, 6th value, f.ex. "2025-05-10 05:00:00": 1.20 via an automation (finally there should be an input form with a button, whitch triggers an automation, where the values (time and amount) should be added to this attribute). Is there a solution for that?
The Input Number integration doesn’t support the creation of attributes. So how did you create that attribute manually?
If you created it by typing it into the editing window of Developer Tools → States then it’s not a permanent addition and will disappear after you restart Home Assistant.
The documentation lists all of the available actions for an Input Number and there are no actions to create an attribute or modify an attribute’s value.