The option “Set up a device nearby” allows you to connect from your phone to another gadget (smartphone or tablet) via Bluetooth for setting. Attention! This requires Android 8.0 Oreo or later (Android 9 Pie or Android 10 Q) to work.
To get started, go to Settings> Google> Set up device nearby.
Beginning of work. Click Next.
Bluetooth on the phone is automatically turned on and it searches for available devices nearby. We connect the device. Once connected, the list of available devices can be viewed here: Settings> Google> Devices.
You can show notifications if a control device is available nearby. Go to Settings> Google> Devices and enable the “Show notifications” option. 
The neighboring device should be within a radius of 30 meters from you, and if these are various accessories (bluetooth headset, for example), then within 1 meter. The other device must be discoverable by Bluetooth, geodata transfer must be enabled.
If your phone doesn't find devices nearby, you may need to add Bluetooth or Wi-Fi pairing first.