So are you saying that when you click on Over Manager (About Manager in English), nothing comes up? That contradicts what you wrote earlier, that the “buttons on top work.”
What I am trying to see is the path to your application data. If you can determine that, I wanted to see the directory for the application data folder. Your problem shows signs of being caused by the program looking in the wrong place for accounting data. This could happen if you changed the default location or moved files. Some files are automatically recreated according to a separate data base in the newest versions. So although you may see businesses listed, they may not be connected to the actual business data files. It can be complex. And depending on how old the backup files are that you are importing, different problems could result.
You might look at this Guide, too:
https://forum.manager.io/t/managing-contents-of-the-application-data-folder/8394