As others have said, encryption is far safer and easier, please consider that path instead if you’re truly in danger of having your ideas read and being punished for it.

However, if you insist, there are tools for what you are seeking. Conlangs (constructed languages) have been used by spies in the CIA and other agencies to converse in plaintext environments in the past. Usually it’s a last ditch effort to communicate in an emergency, but there was that one website that the CIA was using for years before they were finally discovered.

Anyway, there’s sites like this: forgottenlanguages-full.forgottenlanguages.org/?m… It’s weird a fuck, right? Yeah, that site has a lot of conspiracy around it, but the generally accepted thought around that site is it’s a conlang and linguistic hobbyist site. Unfortunately, due to how weird it is, it’s attracted a lot of alien/UFO folk who’ve started shoveling their ideas into the website, so be aware there will be some posts on there that are pretty out there.

Just look up conlang generators and tools, I believe the administrator of that website has emails discussing how they generate a lot of the far out there languages on the site. Think they mention using some python tools, but my memory is rusty.

Good luck. Also, again, please consider using encryption instead.