In recent Fate Grand Order anime (2020), in episode 17 it is said that Tiamat is born without knowing the concept of Death. Will the Mystic Eyes still works on her?
Without a concept of death, Mystic Eyes of Death Perception are useless. They work on the basis that death is an intrinsic part of life, as a living being is meant to end at some point, the concept of death is already inside them, which is what the MEoDP bring about.
From Tsukihime Dokuhon PlusPeriod - TSUKIHIME Dictionary: Mystic Eyes of Death Perception [Unusual talent], p.184:
"(...) Though they are said to see the form of death, strictly speaking it's more accurate to say they're reading the lifespan of a substance – the existential limit determined at the moment of creation(...)"
Tiamat, as a perfect being has no concept of death in herself for the MEoDP to see. You'd have to make her mortal first. For example with a Conceptual Weapon like the Black Barrel which imposes the concept of mortality upon its targets, Gun God uses it against the Types in Notes.