For now I’ve just decided to keep using EagleFiler on the Mac, and either migrate files to it from iOS when needed, or else I use Apple Notes (and Google Keep, and Ulysses) for cross-platform stuff.
I’d love to find a single replacement for EagleFiler (as the dev has expressed zero interest in an iOS app) but with the periodic reports here and elsewhere of sync issues with some apps using iCloud, and my not wanting to upgrade my Dropbox account, I’m content to make do for the time being.
I have Notebooks and the latest version is quite nice, but I’m just really conservative about switching, and I’ve had three good years with EagleFiler (and nine mixed years with DevonNote/DevonThink/DevonThink Pro before that).