What about SeedSigner? Seems to be the best combination, especially when used in a MultiSig setup?

But this is exactly why you do want a purpose built device. I own a 2014 macbook pro and started using crypto currency in 2017. I started with shitcoins, now I'm only bitcoin. But regardless I had a wallet file saved to a USB stick but one day, I checked my funds and they were gone. I consider myself pretty computer literate and to this day, I still don't know how my wallet was swept. Was this laptop air gapped as you're proposing? No, but IMO that is way easier to fuck up than just using a HWW.

SeedSigner has no secure element and uses a Raspberry Pi.

It's not just a problem of individual juicy targets, if people start using airgapped laptops, we will definitely see an increase in attacks on Tails, Sparrow, etc.