Minimize Eyelink window after setup

Coding
1

I am trying to add Eyelink to a simple experiment on Windows 10 in Psychopy 3.

It manages to run through the calibriation and validation processes in Eyelink.
But after the Validation is accepted, the screen remains grey.
I tried several things. As print statements, say it has run through

win.winHandle.maximize()
win.winHandle.set_fullscreen(True) 
win.winHandle.activate()
win.flip()

but nothing happend, I would appreciate some help.
This is the code I am using so far.

from psychopy.iohub import launchHubServer
from psychopy.core import getTime, wait


iohub_config = {'eyetracker.hw.sr_research.eyelink.EyeTracker':
                {'name': 'tracker',
                 'model_name': 'EYELINK 1000 DESKTOP',
                 'runtime_settings': {'sampling_rate': 500,
                                      'track_eyes': 'RIGHT'}
                 }
                }
                
io = launchHubServer(**iohub_config)

# Get the eye tracker device.
tracker = io.devices.tracker


win.winHandle.minimize() #minimize the PsychoPy window
win.winHandle.set_fullscreen(False) # disable fullscreen
win.flip() 

r = tracker.runSetupProcedure() # run eyetracker calibration

win.winHandle.maximize()
win.winHandle.set_fullscreen(True) 
win.winHandle.activate()
win.flip()

Currently I am adding the iohub_config manually, because loading the file hasnt worked until now.

Any help would be appreciated!
Helene