Tested on a UniFi Express, which comes with a preset IP address of 192.168.1.1. Note that the Express is limited to managing 5 UniFi devices, including itself.
Go to Networks: https://192.168.1.1/network/default/settings/networks
Click "New Virtual Network"
Set Network Name and Gateway IP/Subnet as desired
Next to "Advanced" click "Manual"
Set VLAN ID as desired
Check "Network" next to "Isolation" → click "Add"
Go to WiFi: https://192.168.1.1/network/default/settings/wifi
Click "Create New"
Set Name and Password as desired, and set Network to VLAN created above.
Optionally enable "Client Device Isolation" under Advanced → Manual
Click "Add WiFi Network"
Go to Landing Page settings: https://192.168.1.1/network/default/hotspot/portal → "Settings" (This page was not discoverable via "Search Settings" using the terms "landing", "hotspot", "portal", or "guest".)
Under "Landing Page Settings", uncheck "Show Landing Page" → click "Save"
/misc | Jan 20, 2024