I'm glad you've found your way here in the Community, @mieszko-kruger-g.
I have some troubleshooting steps to share so you can get past this hurdle and be able to open your account in QuickBooks Online App.
Let's try resetting the QuickBooks Online App. This is to refresh the data and ensure that new transactions will be loaded. It will also help us clear out the stored files which impact and causes problems in the system.
Here's how:
- Click Help on the navigation bar at the top.
- Select Reset App Data.
- Allow a moment for the process to complete, and then close the app.
- Be sure to right-click the app and Run as Administrator when re-opening.
Once completed, re-open the app and log back into your QuickBooks Online account. If the issue persists, you can try uninstalling and reinstalling the app. You can read through this article to learn more about the features that you can access in the mobile app: Compare mobile app features.
You can check this link about system requirements in the mobile app, and on what is browser works best with QBO: System requirements for QuickBooks Online.
If you have questions about this or need anything else, you can find me here. Have a great day.