Killing an entire race destroying the universe etc.

The former is genocide

Omnicide is killing all life in existence, i.e. Ego from the MCU.

Or killing a whole galaxy (I.e. Darth Vitiate)

Or annihilating the entire multiverse I guess? (I.e. Infinity Ultron, Kang the Conqueror)

Eating Entire Galaxy (Unicron)