I really hate excusing billionaires in their private jets, but you could argue they do not have the money to make a difference in this case.

Technology improves efficiency as time goes on but the biggest change under airline control is switching over to biofuel so at least the carbon emissions are currently active carbon rather than adding carbon that had been sequestered for hundreds of millions of years. So biofuel exists and I believe has been approved, perhaps even internationally, however not much is made and it’s expensive. Private jets can’t spend enough to change that. We need commitments from major airlines to spend enough to invent biofuel scaling way up, and we almost certainly need government and international pressure or encouragement.

Of course that avoids the argument whether private jets are an excess the greater we can afford. And that avoids the argument that the rest of us need investments in rail so we have an alternative