Sharing for anyone else not familiar with AT Protocol:
The AT Protocol is an open, decentralized network for building social applications.
Account portability and Scalability through activity aggregation
Bluesky uses AT Protocol. The connected network/platform is called the Atmosphere.
Bluesky Social has pledged to transfer the protocol's development to a standards body. - Wikipedia
I didn't see any mention of other software/platforms using AT protocol on the protocol website or Wikipedia.
It would certainly be an issue if you didn't have one