Sort of. There isn’t another platform to migrate to at the moment. But this link explains how to self-host your data (PDS) https://atproto.com/guides/self-hosting
And in general, because of the way the protocol works, you could easily build a new app and just use the data that Bluesky wrote. So another platform wouldn’t even need users to “migrate”, since it’s “being your own data”
Maybe you can be the one to build it!
My guess is that nothing yet exists because A) the official app is generally pretty good and B) Bluesky is pretty newly popular so the demand wasn’t there yet