Lingering potions of instant healing, and consequently, instant damage, do not give their respective effects once thrown.
MC-182447
Lingering Potions of Healing and Damage Don't Work
Resolved
Awaiting Response
0
They do however work for me in 20w18a. This means you should provide additional information such as a video showing you throwing a potion. You may also want to add information about your operating system and Java version, whether you were playing in sigle- or multiplayer.