I should explain my bitcoin core with a bit of a bitcoin and my electrum with a bit of a bitcoin.
Both are on the same airgapped machine.
Wait, you already have an airgapped setup with Electrum and Bitcoin Core on it? How did you set that up if you don't mind me asking, since you are now asking questions and looking for advice about how to spend from an airgapped wallet?
So maybe just to dump the priv key and import to electrum will be okay so long as camera cant see it.
Are you looking to import those keys from a different computer or the same one? What is the problem with your current airgapped setup?
Because these wallets have some tx histories I think it maybe possible to start the send tx and sign from the airgapped machine.
A cold wallet can't have a visible transaction history. If that's the case, it means that it was online at some point in the past. If your wallet was online, you don't have an airgapped system and your wallet can't be considered to be a cold one.
I had though if always sending and receiving to the same address you could not have to worry about which input uxtos specifically.
Compare it with paper bills you keep in your wallet. If I pay you $10 with a $10 bill, you now have $10. That's one UTXO. Someone pays you again, that's another UTXO. You can put that bill next to the other $10 bill in your wallet, or you can put it in your back pocket. If that's all the money you have, and you need to pay someone $15, you are going to have to use both bills. The one in your wallet is address #1, address #2 is in your pocket. Doesn't matter if the bills where next to each other (in your wallet) or in different places, you'd still have to spend both to buy something worth $15.