Things I think should have true damage if they must:

Void champs - sure they’re from a different realm maybe they’re powered differently.

Olaf and sett - they have to sort of trade their hp for the damage which makes playing better. Imagine you take 100hp to Olaf e and they take 50dmg due to mitigation then that spell is useless.

Executes - true damage sure, it’s more like threshold so perhaps not true damage.

Damage amplification- there’s no other way to amplify this. If you say this makes to others do 10% more damage but then have to factor resists it might only be 7%. That’s hard to calculate as a player.

Things that shouldn’t be true damage

Darius ult - it’s still just his axe, should he physical damage.

Gp passive - it’s just regular fire

Ksante - not sure why he needs it

Twitch passive - it’s just poison