The cover letter is certainly the most difficult part of an application as it is intended to arouse interest, just like the introduction in a book.
In the cover letter, for example, it is interesting for us to find out why you are applying.
In which direction would you like to develop, in which areas do you have special knowledge and experience or which activities and tasks motivate you.
In this connection we do not expect you to win the next Pulitzer Prize in literature with your cover letter.
If half a page is enough for you to express what is important to you, then it is absolutely all right for us!