My iPhone hot wallet preference is Breez, as it's self custodial and has the lowest LN fees to setup a channel. I don't know anything about the team though, which I like to know whether or not they're decent people.
If QR code doesn't work, I'll research how to manually do it.
You can't Air-Gap a lightning client if you're up to its lightning features.
You can't create a watching-only wallet in Breez using Electrum's master public key either.
You can only create a new wallet or restore from online backup from Google drive or your preferred server.
I think I just learned recovering mnemonic/seed phrases need atleast 1 transaction, as my test cold wallet recovery tests fails with Electrum and Sparrow.
That isn't actually necessary "
technically" since all the client has to do is to derive the private keys from the seed to restore the wallet.
It requires some CPU processes, not internet (
that's for syncing to check for transactions).
That '1 txn requirement' is just a method of some clients to auto-detect which of the standard derivation path and script type the owner of the seed phrase has used.
In your test in Electrum, you must have used "
Detect Existing Account" for it to require a transaction since that button searches from multiple derivations paths to see which ones are already used.
Using the script type selection after pasting your BIP39 seed should be sufficient to restore the wallet if the correct option is selected.