Any wireless router will do this, they don’t need to be connected to the internet to establish a wireless LAN… though I’m not quite following the use case and why you’re specifically requiring a disconnected config.

You may even be able to do it with just your PC, since your PC can act as a hotspot/router and create a wireless LAN… I’ve not done it in recent Windows versions but my fear is in the name of making it easy to use they dumbed it down by making you have one working connection you want to share with other devices… you used to just be able to spin up a Wi-Fi network from your PC. Maybe someone here knows more about that.