Yes.
I assume that the default configuration is that London has the control of your server so they can push updates at will, but client requests go directly to your server and don’t touch London. But I also assume that the enterprise plan can be customized to whatever needs you have, can be as isolated as you need and can be configured for updates however you need.
It depends from what you mean by complex server hosting.
You can create your app on the online IDE, clone it and install it on your own open source Anvil server, then you can manage your own server, and that can be air-gapped.
If you need it air-gapped, use the open source server.
Pros: it’s free.
Cons: you need to manage it yourself.
If you need it not complex, use an enterprise plan:
Pros: it’s easy, Anvil will manage upgrades, security and everything you need.
Cons: it costs more than free.