Hello @Saïda BEN SLIMEN ,
your IoT Hub seems not to able to show the list of devices.
Did you check the Service health page already?
Or check this page.
I cannot reproduce your issue on my IoT HUbs but I've seen this same issue in the past. Then, I just had to wait a few hours and then it worked again.
I remember this was only an Azure portal issue in my case.
I was still able to eg. create a new device using the command line (az) interface:
az iot hub device-identity create -n {iothub_name} -d {device_id} --ee false
This results is a new device:
Using the AZ command on the azure command prompt, you can also list available devices.
If you want to contact Microsoft about this, you can start with sending a message to Azure Support on Twitter