I, also, was a fan of Zim’s clever and elegant way of handling the file system !
There is a plugin that aims to offer the same functionality : xpgo/obsidian-folder-note-plugin: Plugin to add description note to a folder for Obsidian. (here on the forum : Folder Note Plugin: Add description note to folder)
It’s not quite there yet, in particular you have to click to ask for a specific note to turn into a folder note, it’s not as seamless as Zim.