How does this impact AT Protocol? I’m just hearing about AT now, so I’m not familiar

Today, not so much. But once the day is here where we have CRQC, if ATProto hasn't yet started using post-quantum cryptography for identities, users are either vulnerable or a bunch of stuff will break once they push a hotfix to make users not vulnerable.

Alternatively, they fix these things now, so once CRQC arrives, it's already not a problem, and no gets compromised nor have to urgently update their software.