The thing is the Trezor hardware wallet is not an airgapped hardware wallet it requires an internet connected wallet like electrum
I don't understand why you have to have internet to sign something, for example Jade doesn't need internet to sign either...
Theoretically it should work that you connect the Trezor with an airgap Electrum so that you can sign without internet or am I wrong?
But if you’re going in for a maximum security then go just use the electrum wallet on airgapped device and create another watch only device for broadcasting of transactions, this setup doesn’t need a Trezor or any other hardware wallet between them.
But I would like to set up a multisig...