Hey @Jeff_Peterson welcome to the community!
BLUF: Yes, you can use Aptible to host Retool. It's not a preferred method, but should still work.
The instructions for hosting Aptible were removed because we don't know how to maintain an Apitble template and we were often unable to help customers who ran into issues deploying it. The support for multiple container types also made it difficult to support a scaled retool instance. We removed the instructions in an effort to provide clearer guidance on installations with a well defined 'happy path'. That being said, Aptible should still work, we just don't have as much ability to support and troubleshoot those deployments. Our documentation is now just a bit clearer in that regard. Let me know if you have any other questions!