- atproto requires a DNS name (and the TXT record points to a DID which points to a PDS)
- activitypub requires a URI (which in most cases you just HTTP GET directly, optionally following HTTP redirects)
- you could satisfy both by assigning subdomains or letting users bring their own domain
so alice.social.example and https://alice.social.example could be used ~equivalently, but https:// social.example/alice wouldn't work as an atproto identity.