Could Stormbreaker Break Cap's Shield?

We also know that vibranium has a limit, considering Thanos' fingers cracked Vision's forehead, and Stormbreaker buried itself on Thanos' chest. Thor's axe has abilities of its own and could probably break caps shield easily.

Can Mjolnir break Captain America's shield?

Captain America has blocked Mjolnir before - as the hammer has done damage his shield in past battles - but in this case, the vibranium weapon stops it in its tracks. After Thor pulls Mjolnir away from Steve Rogers, Cap's shield is left with scuff marks as smoke is seen from the impact.

Why can't Mjolnir break Cap's shield?

Thor's hammer, Mjolnir, cannot by itself, destroy Captain America's shield. It cannot even dent Captain America's shield. Mjolnir is a magical weapon, imbued with incredible physical and magical properties but none of those powers can destroy Proto-adamantium.