Get your amateur radio license, it has never been easier and radios cheaper. If the internet goes down, it won’t matter if your email and chat app is secure because it won’t work.
What you say is correct, but it’s irrelevant. Whether you use radio or the internet, anything you send can be detected and decoded. Using techniques like FH or DS spread spectrum makes it much harder to do the detection but there are tradeoffs there too. The only unbreakable form of encryption is a one-time pad, IF it is used correctly. Problem is, it’s a pain to use it correctly.
The best method I can think of using technology available to non-governmental users is to layer one form of security on top of another. For example, if you use FHSS to transmit the message, the interceptor first needs to know the FHSS pattern in order to intercept all the pieces. Then maybe obscure the message using steganography, and encrypt the concealed message using something like PGP. Boxes within boxes...
I just don’t have anything to say that needs that much privacy...