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 even internet (
that's for syncing to check for transactions).
It's 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.
Using the script type selection after pasting your BIP39 seed should be sufficient to restore the wallet if the correct option is selected.