Yes it is like that for wallets on airgapped device and airgapped hardware wallets. But Trezor and Bitbox are not airgapped hardware wallets.
hmm so only Coldcard & Passport remains as an airgapped wallet which are open source.
Unfortunately, SeedSigner doesn't work with Electrum & Jade signs airgapped, but Firmupdate cannot be installed airgapped.
Is it possible to connect Trezor & Bitbox to the WatchOnly Wallet so that I can sign there, and then I do the final signing on the airgapped computer (Electrum Coldwallet)