Aircraft fuel is pretty much untaxed in most countries in the world.
Since a plane can easily fly from country to country, any country who taxed airline fuel would simply deter planes from visiting.
Probably the biggest climate move that could have happened at COP26 would have been a global agreement on $1/liter aircraft fuel tax. But it didn't happen.
The 'race to the bottom' argument against all taxes is mostly insignificant: First, airports, air traffic control, etc. have to be paid for somehow; taxes are how it's done. Second, taxes don't determine profits to that extent. Will an airline discontinue service to the EU because of a gas tax?
On many routes, even a small gas tax would just make airlines fill up their tanks at the other end of the journey and carry extra fuel in one direction.
Since a plane can easily fly from country to country, any country who taxed airline fuel would simply deter planes from visiting.
Probably the biggest climate move that could have happened at COP26 would have been a global agreement on $1/liter aircraft fuel tax. But it didn't happen.