For android I tend to like Safe Notes. It’s relatively simple, encrypted with either passphrase or biometrics, and stored locally, with a way to back up to a file. Just make sure you memorize/save the passphrase so you don’t lose your entries. It’s android only though, if that matters. I only use it for shorter stuff, so I’m not sure how well it works for longer entries.

There’s also clauses about revoking your license if you try to sue them, and how you need to still include the system to pay them in your modified version.

I’m pretty sure most screen readers and stuff like copy/paste would also get whatever nonsense you filled it with.

A lot of the ways they scrape documents are the same used by accessibility tools, so I’d generally recommend against doing this.