This is something I would like to get clarification on whether it's intended or not, since it doesn't actually appear to have been reported before (despite being in the game since at least 1.3).
Player-thrown splash and lingering potions of harming (or healing to undead mobs) will deal knockback to mobs caught within the damage radius. As splash potions do magic damage instead of being a physical attack, it seems logical that no knockback should be dealt.
This is also inconsistent with throwing splash water bottles at Blazes and Endermen, which causes no knockback (although it may cause the Enderman to teleport).
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Affects 1.19.1, also this makes lingering potions even worse which boggles the mind that that's even possible
This also applies to harming potions thrown by witches, fired by dispensers, or summoned with /summon. It doesn’t apply if the effect is given to an entity directly using /effect.
I primarily tested with Instant Harming I potions, so higher levels or lingering potions may act differently in some cases.
This is also inconsistent with throwing splash water bottles at Blazes and Endermen, which causes no knockback
I presume this was changed at some point, as blazes, endermen, striders, and snow golems all currently take knockback from splash water bottles. The history section of the blaze’s wiki page states this was changed in 1.14-pre 3, though I could not find any other reference, source, or bug report for this.
Also affect the lingering effect cloud and potion of healing(undead mobs).