Hi AT69,
Welcome to the forums!
You might have seen the other threads relating to OnlyOffice. In one of them, Aristid solved the problem by re-installing the app again. The first time it had no success, the second time it did.
Hope that helps for you as well.
PS: Please consider reading the template/help that is in the window when you start a new support thread. Answering the questions helps others help you, and makes a solution to your problem relevant for others with the same problem.
Secondly, in your screenshot, there is a hint on how to get help: “Provide the full log of this operation by clicking here to get help”. The link anonymizes your log and uploads it to Yunohost so others can easily read (and copy) it.
Good luck!