First Steps" introduced the most powerful being in the MCU -Franklin Richards – and was pretty nonchalant about it.

Franklin’s powers allowed him to create the universe, dimensions, avoid mind control, and every other cool power you can think of. Franklin Richards is considered a Beyond Omega Level mutant, and he is the only one in that category, making him the most powerful mutant on Earth.

First Steps introduces plenty of characters to the MCU, but its strongest one isn't Galactus or Franklin Richards.