Playing on a snapshot realm, (In snapshot 24w09a) and harming potions do not work.

Drinkable, Splash, and Lingering harming potions were not damaging the player.

Harming tipped arrows did seem to be working as normal.

I tested harming potions in a single player world, and they seemed to be working fine there too.

Instant health potions are also working on the realm.