Is there an iOS app for plain text files (Markdown apps are okay, of course) that implements its own searching and doesn't just use Apple's search controls?

So that I can search for strings (bonus points for wildcards or regexp) in all the files in several folders and then lets you open the file at that point.

I'm using FS Notes[0] which does this.

[0] https://fsnot.es/

I do this, but the great thing about Obsidian is easy access to that single file from all your devices.