LNG is not currently a viable green alternative just like Hydrogen isn't.

There is no limitation of either chemistry or physics that would prevent totally green LNG from becoming a thing, like there is for practical hydrogen stroage for transportation.

And many of the limitations you mention of ammonia can be overcome by adding a small percentage of hydrogen to the fuel mix. A much more ready to go alternative than hydrogen alone. And the hydrogen can be obtained by cracking the ammonia itself as needed as part of the engine system's operation, using waste heat.

https://newatlas.com/aircraft/aviation-h2-ammonia-fuel-jet-aircraft/