How to defeat Thanos in the MCU

Thanos is a universal threat so,

You go multiversal.

Doctor Strange (2016) introduces an artifact known as The Staff of the Living Tribunal.

If there is a staff, then there is a Living Tribunal. A nigh-omnipotent being who maintains equilibrium within the Marvel multiverse.

If you can find an emissary to intercede for you, then he can potentially nullify the damage Thanos does in Marvel - 199999. He can't kill or eradicate Thanos coz he's vital for the MCU, but he can reverse his doings. That should be enough to keep him in check.

For an emissary, who else but the Sorcerer Supreme himself.