In UiPath Assistant we have an implementation, that if an error occurs, then Assistant should focus to notify the user.
In Service Mode, the UiPath Robot service is registered and is set to Automatic (Delayed Start).
The UiPath Robot service can take a few minutes, depending on the machine, to start on machine startup. While this happens, UiPath Assistant starts and tries to communicate with the service and encounters the error that it can’t find it, leading to Assistant being focused to notify the user (see screenshot with Assistant, the top right red dot).
The difference is that if RegisterService is not used (User Mode robot), the robot process starts at the same time as Assistant and will remain in the tray because no error is encountered.
For the Service Mode robot, in services.msc, you can try to change the Startup Type to Automatic. This will force the UiPath Robot to start in top services in the system startup and this can help the Assistant to not be in focus when the connection to Orchestrator is not up and running yet.
Try this approach also and let us know the results.