certain aviation fuels still have TEL because they haven’t found anything else that works in those applications yet.
They have finally found a replacement. A company called GAMI got approval for replacement of 100LL in all engines in 2021. No modifications are necessary, aside from a sticker. It’s called G100UL. They’re ramping up production, it’s only available in a few airports atm.
Of course it could’ve been replaced decades ago if the political will existed to ban it, but 🤷♂️