Maybe MCU Zombies operate differently.

The Marvel Zombies from the comics were never mindless.

Zombies operate differently in anything they’re in.

Some zombies can run (World War Z, I Am Legend), others can’t (The Walking Dead)

Some can speak, or at least mumble as a reply (Army Of The Dead), others can’t (most Zombie films/tv shows they can’t)

Some Zombies can get pregnant, or at least carry a child in their womb even if they become zombified (Dawn Of The Dead, Army Of The Dead), others can’t.

Well I wouldn’t really know. I hardly read comics these days. I prefer TV and movie adaptations.

Traditionally, Zombies were undead risen through magic, and they served as slaves to whomever resurrected them. They were mindless, but not violent. They didn’t feast on brains or flesh.

Zombies as we know them today (beings are turned due to a virus that is spread through being bitten) originated from the mind of George Romero in Night of the Living Dead.

So the lore in both this series and the comics are closer to Hollywood than traditional stories.

Are they supposed to be so fragile? Okoye sliced Zombie Sam in half with a Dora Milage spear and Bucky sliced Zombie Cap in half with Cap's shield.

Again, it depends on how they are define in story. Often they are portray as being fragile, like a limb easily falling off, but no blood.

@Jagan raj You say that as if those weapons are toothpicks? They’re both made from the strongest metal on Earth lmao

Zombies in What If...? are formed due to a quantum virus (which is impossible and convoluted). So, I don't think trying to argue too logically about the zombies is wise.