You need to set up a homepage for the device so that everyone who uses it will have the same homepage in Guest Mode.
If you need a homepage that will apply to the device regardless of who uses it, you can set the device to managed guest session by following the steps described below:
- Go to Devices > Chrome > Settings > Managed guest sessions.
- Choose the organizational unit of the devices.
- Make sure that you allow managed guest sessions.
- Search and set up the homepage.