Freedom of speech includes, as a subset, the right to speak in encrypted speech.

  Wf4SyiBipCvf1+w4LbZVmvTQTknq4OtvI+QV60KAPL88U2BbTvHfPM7TRn0Nl+0kTvI+zjMZdTVp7fDaexcgRoGSOZl1TUsoJOrlygrvCuQlmMCx0GHgBo5i8/jnf4kXSyL8RCIUsiS9A86DNBmcdmTqnVdIykIbVdKZkR+e4df7bq40fBTpF2EvEhG8d9UycGaCK3ULNl4qS+zXtjT/MPTDK2zPZJKon3851a9PboFqhY1jlrI6iL0Z7/LT6+iffhUHNtF0wu/hMKKYr4HkN6iUra8HlpqjFnZ8N3aBpN62hT3zdaEIZg8rqkiHcM9bFmMubaVZZgdqtJuEQK3yYY+Iuj6K/7a7eZLqBWU0DK6lOY/BJIKeg0hRlCnTCk3D2uuWeJCX1SzEdH2jw+RVI2ywd9cIw7Bw/GSnR5WLuxHJSrU55768w0rBfYDFQGfIB/RCLZlyu3eID/v7LJWSUA==

The First Amendment, ostensibly AES-encrypted via https://www.gillmeister-software.com/online-tools/text/encry... using the password 'speech'

Indeed. You could take the analogy a step further in that if you add the government as an additional party in the conversation, it's compelled speech because they're forcing you to communicate differently.

The first amendment has been ruled to allow restrictions on the time, place, and manner of speech, as long as those restrictions are content neutral.

I suspect you could find reasoning in the 1st and 4th amendment that protect encryption. Freedom of Speech would apply to encrypted to or unencrypted communications because you're free to speak in whatever format you choose. It doesn't say that encrypted speech is excluded, so it can only be assumed that it is included.

But you’re assuming that encrypted speech only contains its decrypted meaning or even that its decrypted version means anything. Maybe I want to speak the encrypted text. Maybe an encrypted message is what I want to communicate. Imagine an encryption/coding scheme where the cipher-text looks like normal speech but doesn’t mean what it seems like it means... hopefully you get the idea.

I still don't see how in this encryption scheme you could make the case it isn't allowed by the 1st amendment.

Because you wouldn't be free to speak encrypted messages?