The app disappears. It may be that the IP address of the Raspberry Pi you are trying to connect to is incorrect, or the mobile WIFI is not connected to the router. It means that your mobile app and Raspberry Pi are not connected successfully
Connect to the Raspberry Pi using putty and run appserver.py manually. You can run it using the command
sudo python3 adeept_picar-bv2.0/server/appserver.py
Then you can try to connect the Raspberry Pi with the app.
Hmm seems the port is 10223 not 10123 as in the instructions not that it helped the gamepad type interface that appeared has no effect at all on the rover
If you want to control the robot with a mobile phone, it is recommended to run the webServer.py program, and then visit the "Raspberry Pi IP + port number 5000" on the Google browser on the mobile phone, for example "192.168.3.230:5000"