Do you know about Obsidian? I only use it on desktop but I think they have an iOS app as well.

You can use it for simple note-taking but it allows links between your notes so that ideas don't get siloed into folders. It's the ultimate "let your ideas have sex" app because of how you can keep finding connections between them. For instance, you can easily apply a framing in one subject to a problem in another e.g. applying permaculture principles to a particular economic issue AND to a favorite philosopher quote AND to a parenting challenge - without copying the the permaculture notes or moving them.

People have developed a ton of fun ways to use it (one of the only reasons I still use YT!).

I think I saw that there might be a Nostr app that's similar but I haven't looked into it yet.

Also you keep your notes on your device rather than on an Obsidian server (last I looked).